Fasta: remove pedantic_with

It's not used anywhere except a test, and it's definition was not
particularly useful.
Fasta.Tags: remove 'common' type by merging into t
Fasta.Tags: inline char_sequence definition
fasta.mli: factor raw_item definitions to their own section
Fasta.Transform: slight cleanup of raw_item parsers

Eliminate use of Lines.Transform.make as requested in #73.
Fasta: all whitespace lines now treated as empty lines
Fasta: parsers now enforce `max_items_per_line
Fasta: add position information to more errors
Merge branch 'v0.3-dev' of github.com:biocaml/biocaml into v0.3-dev