minor fixes

Minor fixes and cleanup. First release that requires Emacs 24.3.

• increase lookback (#98), fixes #5

• fix derived parent mode (#66)

• load LaTeX substitution table as a feature (#93)

• drop support for Emacs earlier than 24.3, use cl-lib (#87), reorganize test framework accordingly (#95)

• remove latexsub alias for julia-latexsub #101

last release for Emacs23

This is the last release that supports Emacs 23.