Truncated float support for SAS Xport files
SAS xport files allow floats to be stored with fewer than 8 bytes, with implicit zeros in the high order bytes.  Currently we only handle full width (8 byte) floats.  This PR adds support for truncated floats.

seems reasonable. can you add a whats note in enhancements.
 merged via https://github.com/pydata/pandas/commit/547750aa5ba5b4a1b5d0cde05cc21e588b30cc27

thanks!
