Add FASTAFormatError to skbio.io
Add basic generator -> fasta writer and tests
generator -> fasta writer now handles blank seq error case
Add skbio.io._base

Moved _chunk_str from skbio.io.phylip to _base and generalized it so that fasta writer can also use it to split sequences over multiple lines.

Added max_width parameter to generator -> fasta writer for splitting sequences over multiple lines. Added tests for this parameter and writing seqs of varied type.
add unit tests for _base._chunk_str
Add tests to generator -> fasta writer for invalid max_width
STY: Add awesome ordinal error message
Add skbio.util.cardinal_to_ordinal
Fix pep8/flake8 errors
Add fasta writer for BiologicalSequence and all subclasses
Add fasta writers for SequenceCollection and Alignment
Clean up sequence testing code a bit
Merge branch 'master' into issue-678
Add API to clean id and description in fasta writer

Still need to add the actual functionality and tests.
Add support for sanitizing ids and description in fasta writer.

Still needs unit tests.
add error case tests for id/description sanitizers
Add tests for description sanitizer in fasta writer (default behavior)
Add tests for description_newline_replacement
Test default id_whitespace_replacement behavior
Finish tests for id_whitespace_replacement