Added secion about project-specific settings to Readme.
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.
projectile-ag: vary prompt based on current-prefix-arg
Merge pull request #403 from offby1/master

projectile-ag: vary prompt based on current-prefix-arg
Merge pull request #395 from joelmccracken/master

Adds examples to .dir-locals.el section in README
Fix a couple of failing tests
Quick fix for a failing test
Fix a broken test
Simplify test init
Fix noflet bindings indentation
Add a test for projectile-clear-known-projects
Replace redundant use of let*
Don't try to switch to a known project if there are no known projects
Extend the changelog a bit
Add a test for projectile-switch-project with no known projects
Remove a bunch of redundant functions to turn on/off projectile
Restore projectile-on as we actually need it
[Fix #406] Add the ability to ignore buffers by name
Remove projectile-on

Using projectile-mode directly should yield the same result.
Add Helm interface to switch project

This is different from simply setting `projectile-completion-system' to `helm'
which only enables projectile to use the Helm Completion to complete a project
name. This commit added new command `helm-projectile-switch-project', and bind
to "H" in projectile command map by default. The new command uses helm interface
instead of ido to switch project. The benefit of this approach is that on any
selected project we can fire many actions, not limited to just one action of
"switch to project", as in the case of using helm completion by simply setting
`projectile-completion-system' to `helm'. Currently there are only three
actions, namely "Switch to project", "Open Dired in project's directory" and
"Switch to Eshell", but will definitely add more in the future.

A new helm source `helm-source-projectile-projects' has also been added, and
this source has been added to `helm-projectile-sources-list' so that one can
also run `helm-projectile' to switch project.