Implement commands for configuration of filters

Two new commands: git media install, git media uninstall.
The commands installs or uninstall the clear and smudge filters.
This automates the git media  operations so they are performed automatically
when using git in a normal workflow.

Filters are put in the local repository config file (.git/config)
pass through and print warning if clean filter detects a hash
Merge branch 'auto_configuration' of https://github.com/rickyah/git-media into bugfixes