Some changes to the location feature

* StringScannerKramdown → Kramdown::Utils::StringScanner
* The class now takes the start line number as optional second
  argument.
Disable warnings on test runs because of Prawn
Fixed PNG generation with gnuplot
Fixed problem with uninitialized start line number
Updated release notes, version and homepage
Added direct PDF output to main landing page image
Added missing arrow
Added travis configuration file
Some travis fixes
Some more travis changes
Add rake dev:gemspec task to allow users of bundler to use a local (or, if the gemspec is commited) a specific remote version of kramdown..
Alias 'dev:gemspec' to 'gemspec'; add 3 file dependencies.
Merge branch 'master' into gemfile