TST: move Styler format tests to own module
The following tests moved from `style/test_style.py` to their own module `style/test_format.py`.

def test_display_format(styler):
def test_format_dict(styler):
def test_format_string(styler):  [added new]
def test_format_callable(styler):  [added new]
def test_format_with_na_rep():
def test_format_non_numeric_na():
def test_format_clear(styler):
def test_format_escape():
def test_format_escape_na_rep():
def test_format_escape_floats(styler):
def test_format_raises(styler, formatter):
def test_format_with_precision():
def test_format_subset():

The new module does not use `class` setup structure.


Hello @attack68! Thanks for opening this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:

* In the file [`pandas/tests/io/formats/style/test_format.py`](https://github.com/pandas-dev/pandas/blob/89813271c12fbb72a9d43667af01e372c2b10206/pandas/tests/io/formats/style/test_format.py):

> [Line 32:89](https://github.com/pandas-dev/pandas/blob/89813271c12fbb72a9d43667af01e372c2b10206/pandas/tests/io/formats/style/test_format.py#L32): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (91 > 88 characters)
> [Line 34:89](https://github.com/pandas-dev/pandas/blob/89813271c12fbb72a9d43667af01e372c2b10206/pandas/tests/io/formats/style/test_format.py#L34): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (97 > 88 characters)
> [Line 38:89](https://github.com/pandas-dev/pandas/blob/89813271c12fbb72a9d43667af01e372c2b10206/pandas/tests/io/formats/style/test_format.py#L38): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (98 > 88 characters)
> [Line 43:89](https://github.com/pandas-dev/pandas/blob/89813271c12fbb72a9d43667af01e372c2b10206/pandas/tests/io/formats/style/test_format.py#L43): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (120 > 88 characters)
> [Line 72:89](https://github.com/pandas-dev/pandas/blob/89813271c12fbb72a9d43667af01e372c2b10206/pandas/tests/io/formats/style/test_format.py#L72): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (90 > 88 characters)



 > Hello @attack68! Thanks for opening this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:
> 
> * In the file [`pandas/tests/io/formats/style/test_format.py`](https://github.com/pandas-dev/pandas/blob/89813271c12fbb72a9d43667af01e372c2b10206/pandas/tests/io/formats/style/test_format.py):
> 
> > [Line 32:89](https://github.com/pandas-dev/pandas/blob/89813271c12fbb72a9d43667af01e372c2b10206/pandas/tests/io/formats/style/test_format.py#L32): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (91 > 88 characters)
> > [Line 34:89](https://github.com/pandas-dev/pandas/blob/89813271c12fbb72a9d43667af01e372c2b10206/pandas/tests/io/formats/style/test_format.py#L34): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (97 > 88 characters)
> > [Line 38:89](https://github.com/pandas-dev/pandas/blob/89813271c12fbb72a9d43667af01e372c2b10206/pandas/tests/io/formats/style/test_format.py#L38): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (98 > 88 characters)
> > [Line 43:89](https://github.com/pandas-dev/pandas/blob/89813271c12fbb72a9d43667af01e372c2b10206/pandas/tests/io/formats/style/test_format.py#L43): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (120 > 88 characters)
> > [Line 72:89](https://github.com/pandas-dev/pandas/blob/89813271c12fbb72a9d43667af01e372c2b10206/pandas/tests/io/formats/style/test_format.py#L72): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (90 > 88 characters)

This is quite odd since these lines are not long and don't have more than 88 chars in them!?  > > Hello @attack68! Thanks for opening this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:
> > 
> > * In the file [`pandas/tests/io/formats/style/test_format.py`](https://github.com/pandas-dev/pandas/blob/89813271c12fbb72a9d43667af01e372c2b10206/pandas/tests/io/formats/style/test_format.py):
> > 
> > > [Line 32:89](https://github.com/pandas-dev/pandas/blob/89813271c12fbb72a9d43667af01e372c2b10206/pandas/tests/io/formats/style/test_format.py#L32): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (91 > 88 characters)
> > > [Line 34:89](https://github.com/pandas-dev/pandas/blob/89813271c12fbb72a9d43667af01e372c2b10206/pandas/tests/io/formats/style/test_format.py#L34): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (97 > 88 characters)
> > > [Line 38:89](https://github.com/pandas-dev/pandas/blob/89813271c12fbb72a9d43667af01e372c2b10206/pandas/tests/io/formats/style/test_format.py#L38): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (98 > 88 characters)
> > > [Line 43:89](https://github.com/pandas-dev/pandas/blob/89813271c12fbb72a9d43667af01e372c2b10206/pandas/tests/io/formats/style/test_format.py#L43): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (120 > 88 characters)
> > > [Line 72:89](https://github.com/pandas-dev/pandas/blob/89813271c12fbb72a9d43667af01e372c2b10206/pandas/tests/io/formats/style/test_format.py#L72): [E501](https://duckduckgo.com/?q=pep8%20E501) line too long (90 > 88 characters)
> 
> This is quite odd since these lines are not long and don't have more than 88 chars in them!?

maybe the bot is having an off day :-< thanks @attack68 