Myokit

- Added hyperbolic functions to CellML import.
- Updated cellml import: Unused variables without an rhs are now removed, used variables without an rhs are given an automatic rhs of 0.
Both cases generate a warning.
- Update to cellml import: If a variable is mentioned but never declared (i.e. if it is an external input) a dummy variable is now created and a warning is given.
- Added method to `myo` to get version number.
- Fixed string encoding issue in CellML import.
- Tweaks to the gui based on workshop feedback.
- Fixed windows issue: IE likes to download `.cellml` files as `.xml,` making them invisible to the gui.
Added a glob rule for `.xml` to the cellml import in the gui.

- Moving to next version.
- Small bugfixes and a `variable.value()` method.

- Various small bugfixes.

- Added a formatting option to the `Benchmarker`.
- Fixed OS/X GUI issues with progress bar.

- Adding Sympy to formats list.
- Added sympy exporter and importer.
- Added `LinearModel` class for working with markov models.

- Now raising exception when user cancels simulation instead of silent exit.
- Added zero-step detection to cvode sim that now raises a `SimulationError` after too many consecutive zero steps.