Fixed require of master-tex-finder.
Adds an auto-find-tex-master feature.

When asked to compile a latex file the package
would now search the current directory for the
master tex file. This is helpful in case the
latex document is split in several files since
it allows compilation from any latex file in
the project.
Fixed fixtures directory structure.

moved fixtures used by master-tex-finder-spec
into sub-directory master-tex-finder.
Improved MasterTexFinder

Now it immediately checks if the given file is
a master file so to avoid the whole finding
process when possible.
Improved MasterTexFinder.

Now it returns a list of master files.
Implements magic comments parsing.
Code cleanup.