DOC: improvements and no dvipng anymore
DOC: Add images, refactor.
Remove useless functions, keep some as internal-only.
Use internal fn.
PY3: fix exception style
Merge branch 'master' of https://github.com/ahkab/ahkab into tests
Relax requirements.
Cache previous results (speeds up simulations).
Merge branch 'master' of https://github.com/ahkab/ahkab into tests