Added options for exec command and a new exec_all command.
Merge pull request #105 from JCook21/ExecCommands

Further work on exec command
Remove homesick commands where "homesick exec" could be used instead

Commands removed:
- commit
- diff
- pull
- push
- status
Replace the following commands with exec aliases: pull commit push status diff
Re-add some of the specs for aliased commands, with some minor fixes
Move git command aliases to the same place in the source code
Update usage for git aliases and rename a variable
Use the awesomeness of metaprogramming to create the git aliases