Miscellaneous grammatical & consistency changes

- Various grammatical changes and rephrasings
- Capitalize names of VCSes and "Bash"
- Standardize references to project name ("Liquid Prompt")
- Use title casing in README section headers
- Use multiple list-levels in README where appropriate
- Fix code block in pull request instructions in CONTRIBUTING

Conflicts:
	CONTRIBUTING.md
	README.md
	example.bashrc
	liquidprompt
	liquidpromptrc
implementing issue #110

as the activation of GIT_PS1_SHOWUPSTREAM option does for __git_ps1
the _lp_git_branch_color now compute how many commit we are ahead or
behind of our remote reference.

Conflicts:
	liquidprompt