Create ryr-simulator-parallel.R

Fixes
- Added '1.0' value to 'nndbreaks' and 'radbreaks'
- Changed 'numPatterns=1' to 'numPatterns=99'
- N is set automatically
- Voxel resolution is set automatically via the appropriate Matlab file
- input and output paths can now be set to any folder, not just the source folder for the simulator package

New features
- Parallel processing capability (requires 'snow', 'doSnow', 'iterators', and 'foreach' libraries)
- Writes a text file with elapsed time and number of cores used
Update ryr-simulator-parallel.R

Fixed a comment
Merge pull request #1 from gbass/master

Created ryr-simulator-parallel.R for parallelised simulation of RyR cluster distributions.