Move Projectile's menu item under Tools.
Introduce support for finding tests and switching between code and tests.

`projectile-find-test-file` gives you a quick way to navigate to test files
within the project. `projectile-toggle-between-implemenation-and-test` gives
you the ability to toggle between the code and it's test file. Currently this
works only for Rails projects using rspec, but it will be extended to support
other popular project types.
Remove projectile-open.
Implement basic project type detection.

The project type detection is based on the project
directory structure and can be used in the future
to select correct compile and test commands and to
intelligently switch between implementation and test files.
Display keymap in a table instead of list.
Use fast external tools to find the files in a project when possible (#56)
Fix #57 - properly set the current working dir, before invoking shell commands
Limit find to search only for regular files
Fix a performance bug related to projectile-expand-root

`projectile-expand-root` calculates the project root on each call, which
is a fairly expensive operation. This function should never be used
on more than a few files.
Remove projectile-reindex-project

It was replaced with easier to use prefix arguments that force
cache invalidation for finding files and tests in a project.
Include untracked files in git ls-files's output.
Fix git ls-files arguments
Several improvements to the external commands backend

* more reliable VCS detection
* customizable external commands
* added a few missing docstring
Fix helm-projectile and optimize its performance
Add a simple version reporting command projectile-version.
Add a customization option to enable native Emacs Lisp indexing of projects
Mention projectile-find-test-file in the README.
if (buffer-name) is nil, use default-directory
Merge pull request #59 from Wilfred/master

Fix crash in projectile-find-file from magit
An initial attempt to run regression tests on TravisCI