Increment the patch number of project

        :var release_tag describes the tag ('a', 'b', 'rc', ...)
        :var release_tag_version describes the number behind the 'a', 'b' or 'rc'
        For e.g.:

def set_patch(self, pre_release_tag=''):
        """
        Increment the patch number of project

        :var release_tag describes the tag ('a', 'b', 'rc', ...)
        :var release_tag_version describes the number behind the 'a', 'b' or 'rc'
        For e.g.:
        """

        current_version = self.get_version()
        current_patch = self.get_patch_version(current_version)
        current_pre_release_tag = self.get_current_pre_release_tag(current_patch)
        current_RELEASE_SEPARATOR = self.get_current_RELEASE_SEPARATOR(current_patch)
        new_patch = ''

        # The new patch should get a release tag
        if pre_release_tag:

            # Check, if the current patch already contains a pre_release_tag.
            if current_pre_release_tag:
                new_patch = str(current_patch.split(current_pre_release_tag, 2)[0]) + pre_release_tag

                if pre_release_tag == current_pre_release_tag:
                    new_patch += str(int(current_patch.split(current_pre_release_tag, 2)[1])+1)
                else:
                    new_patch += '0'

            # The current patch does not contains a pre_release_tag.
            else:
                new_patch = str(int(current_patch)+1) + \
                            APISettings.RELEASE_SEPARATOR + \
                            pre_release_tag + \
                            '0'

        # The new patch should not contain any tag. So just increase it.
        else:
            if current_RELEASE_SEPARATOR:
                new_patch = str(int(current_patch.split(current_RELEASE_SEPARATOR, 2)[0])+1)
            elif current_pre_release_tag:
                new_patch = str(int(current_patch.split(current_pre_release_tag, 2)[0])+1)
            else:
                new_patch = str(int(current_patch)+1)

        new_version = str(int(current_version.split('.', 5)[0])) + '.' + \
            str(int(current_version.split('.', 5)[1])) + '.' + \
            str(new_patch)
        self.set_version(current_version, new_version)