Bam: delete trailing whitespace
Bam: add option gzip_level to raw_to_string
App_common: use gzip_level for Bam transforms
app.demux: fix typo in manual
app.transform: draft manual
Merge branch 'v0.3-dev' of github.com:biocaml/biocaml into v0.3-dev
app.transform: implement SAM-Item → Fastq-Item
Math,Roc: use `~cmp` label for `Array.sort`

This should make Biocaml compile with 109.18.* (issue #89).
Bam: move errors to the `Error` sub-module
Bam: stop exposing low-level functions
Bam: move `parse_{optional,cigar}` to `Lwt_level`
Bam: improve documentation
Bam: define Error.t
Bam: add in_channel_to_{,raw_}item_stream{,_exn}
Bam: add some documentation
Transform: change API of `filter_compose`

The function now uses lowercase polymorphic variants (like the rest of
the code).
The documentation and the figure have been updated too.
Line,Lines: improve documentation
Sam: add `missing in_channel_to_*` functions
Sam: improve documentation and API
Wig: clean-up error types