[Fix #138] Add syntax checkers for Puppet

The first checker, `puppet-parser`, uses puppet's own `puppet parser
validate` command to check syntax. The second checker,
`puppet-puppet-lint`, is chained to the first and uses the
`puppet-lint` program to check adherence to the Puppet style
guidelines.

Add four new unit tests to test single line and multiline error
patterns from `puppet-parser`, and to test ERROR and WARNING error
patterns from `puppet-puppet-lint`.

Update the Vagrant provisioning script to install puppet.
Improve Makefile targets for doc building

Add a separate `info` target to build Info documentation, and let `doc`
build all documentation, that is, Info and HTML.
Add a Texinfo macro to shorten Github links
Build Info only on Travis