Add command line interface to `texparser`

This is the first step to let us parse logs independently from
`texmate`. In the end this change should us allow to use `texparser` in
“LaTeX Watch” to generate gutter marks for error messages and warnings.
Quote messages for gutter marks

Before this change, a message for the gutter containing single quotes
caused an error.
Add message to gutter marks for warnings
Simplify code to set latexmk engine in “LaTeX Watch”