Allow to run grunt tasks on different port

Works on #536
Update README
Merge pull request #539 from latin-language-toolkit/dynamic_dev_port

Allow to specify dev server port as command line option
Add grunt-ngdocs
Ignore docs folder
Add connect:doc task for docu server
Load all packages and arethusa for ngdocs
Add watch:doc task
Add example documentation (not yet working)
Start docu for exit directive
Remove broken examples
Add `grunt doc-server`

Concurrently generates docs, adds a watch for regeneration and starts
the doc server.
Update ngdoc syntax
Live reload the documentation
Update exit directive documentation
Fix type in StateChangeWatcher docs
Documentation for exitHandler and exit
Add a link to the landing page in docs
Try to fix doc anchors

There seems to be something wrong with ngdocs here...
Add customized navbar to docs