Add bowtie2/2.2.3

bowtie2/2.2.3 is an update of bowtie2/2.2.2 with some bug fixes:
- Fixed a bug that made loading an index into memory crash sometimes.
- Fixed a silent failure to warn the user in case the -x option is missing.
- Updated al, un, al-conc and un-conc options to avoid confusion in cases
where the user does not provide a base file name.
- Fixed a spurious assert that made bowtie2-inspect debug fail.

Signed-off-by: James Oguya <oguyajames@gmail.com>