Move compiler settings to its right place

Why was it in directory `impl` and in package `gnieh.blue`????
Add synctex option to compiler settings.

This piece of information is required to implement #15.
Authors may decide for each paper if the SyncTeX data must be generated
upon compilation.
Configuration may also be used to change the default value when a paper
is created.
Add API to retrieve SyncTeX data

This API implements the feature required by #15.
Authors (and only authors) may retrieve the generated SyncTeX data for
any given paper.