Check if some latex output files exist
        before first latex run, process them and return
        the generated data.

            - Parsing *.aux for citations counter and
              existing glossaries.
            - Getting content of files to detect changes.
                - *.toc file
                - all available glossaries files

def _read_latex_files(self):
        '''
        Check if some latex output files exist
        before first latex run, process them and return
        the generated data.

            - Parsing *.aux for citations counter and
              existing glossaries.
            - Getting content of files to detect changes.
                - *.toc file
                - all available glossaries files
        '''
        if os.path.isfile('%s.aux' % self.project_name):
            cite_counter = self.generate_citation_counter()
            self.read_glossaries()
        else:
            cite_counter = {'%s.aux' % self.project_name:
                            defaultdict(int)}

        fname = '%s.toc' % self.project_name
        if os.path.isfile(fname):
            with open(fname) as fobj:
                toc_file = fobj.read()
        else:
            toc_file = ''

        gloss_files = dict()
        for gloss in self.glossaries:
            ext = self.glossaries[gloss][1]
            filename = '%s.%s' % (self.project_name, ext)
            if os.path.isfile(filename):
                with open(filename) as fobj:
                    gloss_files[gloss] = fobj.read()

        return cite_counter, toc_file, gloss_files