Update: make fl_file functions more consistent and update documentation

Update: make fl_file functions more consistent and update documentation

Refactor the fl_file functions.
Rewrite memory management in f_file and fl_file functions.

Fix bug with size of bytes, renaming it to byte_chunk to avoid confusion.
Add block size property to f_file structure to allow custom block size handling (as opposed to the previous behavior of using a hard-coded default).

Make sure f_none_on_eof is actually returned.