Do not de/index None values, and other index stuff

- it the value to index/deindex is None, do nothing
- calls to the index/deindex methods are done only if field is indexable
- replace "if self.indexable" by "assert self.indexable" in these methods
- hset and hincrby use hget and not hgetall to know value to deindex
Merge pull request #76 from twidi/no-deindex-index-none-values

Do not de/index None values, and other index stuff
Add link to source code in doc index page
Remove cache from documentation
Doc syntax proof reading
5 is not 6...
Add egg-info and dist/* to .gitignore
Add a WTFPL licence
Change download URL
Bump version to 0.1.0
Add a MANIFEST.in
Add redis as install requirement
Add install in README
Include only the "limpyd" package in setup.py (no tests)
Merge pull request #77 from twidi/remove-tests-from-package

Include only the "limpyd" package in setup.py (no tests)
Add the missing 'delete' command to the HashField field
Add tests for the delete command for all fields
Add a changelog file