fix issue#9
Derive from prog-mode when available
Improve paragraph filling of block literals

The functionality of this patch can be demonstrated on a small
example. Consider the YAML document below:

    foo: >-
      block
      literal
    bar:

When point is inside the "block literal", pressing M-q
(fill-paragraph) results in:

    foo: >- block literal bar:

This is probably not what most users want. With this patch, the result
will look like in the following:

    foo: >-
      block literal
    bar:
Use the syntax table for highlighting comments.

Fixes https://github.com/yoshiki/yaml-mode/issues/19
Merge branch 'master' of https://github.com/ToBeReplaced/yaml-mode into upstream-tobereplaced
Merge branch 'issue#9' of https://github.com/ekoontz/yaml-mode into upstream-ekoontz
Merge branch 'upstream-tobereplaced'
Merge branch 'upstream-wentasah'
Merge branch 'upstream-wilfred'