Demote errors to messages when trying to load a TAGS file.
Call error if the tags command failed.

Fixes https://github.com/bbatsov/projectile/issues/377
Use `defadvice' rather than the new `nadvice` interface which is only
available in trunk. This fixes f71b5f7.

* projectile.el (projectile-compilation-find-file): Convert to `defavice'.
                (projectile-mode): Use ad-(de)activate.
Added secion about project-specific settings to Readme.
Mention how to add an alternative key prefix for all Projectile commands
Fixed a bug where if you delete a directory that used to exist, it could not find-file-in-known-projects
Fix keymap sorting
Reshuffle keybindings a bit

* Use a common prefix (`s`) for all search commands (`ack`, `ag` and
  `grep`)
* Remap switching to project to `C-c p p` (easier to press)
* Remap testing project to `C-c p P` (perhaps this needs a better keybinding)
Update README.md

The default keybinding for `projectile-switch-project` is C-p p p, not C-p p s
Make projectile-persp-switch-project work from lisp

If not called interactively, takes an argument of the project's directory
Make projectile-mode-line customizable

Do not explicitly set projectile-mode-line, but instead use a standard
mode line format and splice the project name into it with :eval.

Allows users to completely customize the appearance of the Projectile
Mode line.
Suppress a couple of compilation warnings
Adds examples to `.dir-locals.el` README section.

Provies examples for customizing project compilation command string and
project test command string.

Fixes existing example code.

Adds documentation of using `.dir-locals.el` along with defcustom settings.
Add helm as development dependency.
Respect projectile-keymap-prefix when binding helm-projectile.
projectile-ag: vary prompt based on current-prefix-arg
Use a single mode line construct for projectile-mode-line

Multiple constructs break minor mode menus, see 
https://github.com/flycheck/flycheck/issues/365#issuecomment-51463686
Fix a couple of failing tests
Quick fix for a failing test
Fix a broken test