Return a list of GdxSymb found in the GdxFile.

def get_symbols_list(self):
        '''Return a list of GdxSymb found in the GdxFile.'''
        slist = []
        rc, nSymb, nElem = gdxcc.gdxSystemInfo(self.gdx_handle)
        assert rc, 'Unable to retrieve "%s" info' % self.filename
        self.number_symbols = nSymb
        self.number_elements = nElem
        slist = [None]*(nSymb+1)
        for j in range(0,nSymb+1):
            sinfo = self.get_sid_info(j)
            if j==0:
                sinfo['name'] = 'universal_set'
            slist[j] = GdxSymb(self,sinfo)
        return slist