Allow customization of digits grouping space size

https://code.google.com/p/speedcrunch/issues/detail?id=515
Don't insert parens on function autocompletion when changing function name
Add Edit functionality to user functions from dock window

This can be done by either right-mouse click or Ctrl+E on the selected
user function. The full expression, as originally entered by the user, will be
inserted into the editor.
Add Particle Masses constant category

https://code.google.com/p/speedcrunch/issues/detail?id=530

Leptons, quarks, bosons, hadrons...
Allow multiples instances of the application again

https://code.google.com/p/speedcrunch/issues/detail?id=529

Leave the handling to the native desktop, as there are many users who like to
open more than one session simultaneously.
Add some more tests for hmath, covering new known bugs