Quote project root in format string

Without this it's easy to cause an error if the directory name contains
shell syntax. E.g., in bash, try:

  $ cd ~/One (Two) && echo oops
  -bash: syntax error near unexpected token `('

To test the fix I invoked helm-cmd-t from a git repo whose path has a
left paren in it and no longer saw the above error reported in helm.
Fix some byte-compile warnings.
Emphasize cache augmentation by addition more sources.

- #18
Add documentation for cache management.

- #18
Add grep documentation.

- #18
Fix cache invalidation.

- #18
Don't bother caching ftime.

- fixes #19
Get actions from type `file' directly.

- fixes #20
Initial ize buffers source if required.

- fixes #21
Fix unbalanced "(" in previous commit.
Merge pull request #17 from chrisklaiber/master

Quote project root in format string