Closes #49
Closes #50

This allows us to easily run selected checks only.
This also splits the check logic up nicely so that it can be
refactored without affecting the others.

Common tasks such as tokenising the incoming data or finding the starting
tokens of classes has been pulled out of the check logic as well to DRY
things up.

Put possible error levels on next line (80 column limit).
Add separator between global options and --no-[name]-checks.

bin/puppet-lint
* Added the --log-format option.
  Added documentation to the --help output.

lib/puppet-lint.rb
* Check for 'string' % {hash} functionality and basic backport.

* Added helper methods and the log-format configuration option to the main PuppetLint class.
  - log_format:     Gets the configured log-format.
                    Tries to mimic the old behavior if no
                    log-format has been set.

  - format_message: Format the message.

* change @path -> @FileInfo.
  Store more information on the file.

* rewrite the report function.
  - can handle all problem types.
  - updates statistics on each kind (error,warning)
  - merge fileinfo in the message
  - add additional placeholder for uppercase kind (ERROR,WARNING)
  - filters on configured error_level

* changed the run function.
  - heavily simplified since we offload error_level and statistics
    to the report function.
  - expects plugin return values to be a array of { problems }

* Remove warnings and errors attritube -> problems attribute.
* Introduced @default_info
* Removed warn and error and replaced by notify function.
  - notify function merged @default info with the message.
* Adjusted run function
  - set the name of the check in @default_info
  - only return @problems in stead of errors and warnings in a hash.

* Implemented filter_array_of_hashes (helper) function.
  - See source for an example.
* Implemented have_problem check.
  - Checks if a problem exists in the array that matches the filter hash.
  - Add readable failure messages.
* Implemented only_have_problem check.
  - Checks if the problem array only exists out of elements matching the filter hash.
  - Add readable failure messages.

* Checks use its(:problems) now.

NOTE:
 In some cases, I was unsure wether to use

  its(:problems) { should only_have_problem :kind => :warning, :message => "..." }
 or
  its(:problems) {
    should have_problem :kind => :warning, :message => ''
    should_not have_problem :kind => :error
  }

  The first one fails if there are any other warnings and/or errors returned.
  The second one only fails if there are any errors but allows other warnings.

* A small implication is that I removed the linenumbers from within
  the message and moved it to :linenumber. There is now a warning
  that an error occured on a line, but the line number is added
  separatly.
  In some cases, with default (backwards compatible)  formatting,
  this results in "line has more than 80 characters on line 4".
  (Original was: "line 4 has more than 80 characters")