Add new command projectile-commander

It allows the selection of projectile actions with s single key and is
now the default project-switching action.
Add TAGS to .gitignore
Add prefix arg support to projectile-switch-project

When prefix arg is present always invoke projectile-commander.
A few changelog improvements
Enhance the output of projectile-cache-current-file
Bump version to 0.10.0
Fixed the function invoked by "def-projectile-commander-method ?k"
Merge pull request #215 from ngirard/patch-1

Fixed the function invoked by "def-projectile-commander-method ?k"
* Added new `projectile-commander` methods ?v and ?R which run
  `projectile-vc-dir` and `projectile-regenerate-tags`, respectively.
Merge pull request #216 from nwidger/master

Added new `projectile-commander` methods ?v and ?R which run  `projectile-vc-dir` and `projectile-regenerate-tags`
[Fix #221] Add ack and ag to the commander
fix docstring of projectile-file-truename
don't treat Makefile as an indicator of the project root

Sadly, despite recursive make well-known to be harmful, it is still
in common use, which means that the presence of Makefile in a
directory cannot reliably indicate that that directory is the root
of a project.  Therefore it is safer not to include this in
projectile-project-root-files by default.
Merge pull request #226 from aspiers/fix-recursive-make-projects

don't treat Makefile as an indicator of the project root
Modified `projecile-ack` to append options to `ack-and-a-half-arguments`

instead of overriding them.
Update CHANGELOG to indicate fix to `projectile-ack`
Merge pull request #228 from nwidger/master

Modified `projecile-ack` to append options to `ack-and-a-half-arguments`
allow projectile-project-root to find the root for symlinked files

This covers the case where you have a git repo ~/configs (for dotfiles
etc.), and the subdir emacs of that repo is symlinked to ~/.emacs.d

projectile-project-root in a buffer visiting ~/.emacs.d/init.el will
find the root at ~/configs.

It also covers the case of a single file symlinked outside a repo.
Merge pull request #227 from aecay/master

allow projectile-project-root to find the root for symlinked files
[Fix #223] Make projectile-vc-dir magit-aware