show Travis CI badge in README.md
track ALL classes and modules methods simply by setting $automatic_private_please_tracking
better names + move methods + reorder ...
remove the `private_please :foo, :bad` syntax

because tracking a single method is not really useful.
We can track a single class (subset), or all the classes, and that's enough
don't double-require version.rb with Ruby 1.8.7 - fixes #5

this removes the warning
```
private_please/lib/private_please/version.rb:2: warning: already initialized constant VERSION
```
don't redefine NO_CALLS_OBSERVED - fixes #6
require 'set' is necessary when running PP live (not in tests)
code in at_exit in invalid - fixes #8

Travis would complain :
```
/home/travis/build/alainravet/private_please/spec/../lib/private_please.rb:29: undefined local variable or method `candidates_store' for main:Object (NameError)
The command "bundle exec rspec" exited with 1.
Done. Your build exited with 1.
```
doc : simple instructions for developers
fine-tune the moment tracing is started (in auto-mode and in manual mode) - fixes #14
fix loading order error when running PP from command line - fixes #3
include sample files under /doc so the documented examples work as written.
call_initiator can be nil without negative effects - fixes #16
refactor the sample fixtures
improve the default report - #11 and fixes #17
document the bug #22

problem : module methods added via extend are wrongly reported as never_called

How to reproduce :
$ PP_OPTIONS="--show-never-called" be ruby -Ilib spec/fixtures/bug_22.rb
refactoring : move code/rename tests (clarity)
don't track overridden methods - fixes #2
tests no longer pollute the console - fixes #1
test what happens at_exit - fixes #9