Port to Cohttp 0.10.x API

Should be no functional change, but the body handling is now cleaner
Activate annotation files and debug
Bump version to 0.5.1
Rename IrminTree into IrminNode
Fix gitignore
Rename IrminBlob to IrminContents
Update copyright years
bump to 0.6
Update CHANGES
Merge branch 'master' of github.com:samoht/irminsule into cleanups

Conflicts:
	CHANGES
	_oasis
	lib/core/META
	lib/core/irminsule.mldylib
	setup.ml
Merge pull request #30 from samoht/cleanups

Cleanups