Fix HamlCommentNode#text

There were a couple more bugs with this implementation when extracting
text from comments at the end of a HAML document or containing spaces.

Change-Id: Ie525c10403da4d3048a54d605a5cd630e52b3bfc
Reviewed-on: http://gerrit.causes.com/44995
Tested-by: jenkins <jenkins@brigade.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>
Add tests for HamlLint::Tree::Node

This class was started to have some complicated logic in its methods
that are intended to be consumed by linters. Ensure these are working as
expected by adding some tests.

Change-Id: Idf6322d82eb9130b5955a01f7a655c4f2cc5d0f9
Reviewed-on: http://gerrit.causes.com/44994
Tested-by: jenkins <jenkins@brigade.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>
Add specs for HamlCommentNode

Turns out there were still some bugs with this class's implementation of
`text`, so add some tests and fix the relevant bugs.

Change-Id: I450002ea19c54c8edf9236b0f9772a4789c67cb5
Reviewed-on: http://gerrit.causes.com/44993
Tested-by: jenkins <jenkins@brigade.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>