Added user functions support to auto-completion.
Show user functions signatures when the user is using it (the same way as with built-in functions).
Bumped the session export format version to 0.12 (instead of 0.11).
Fixed a bug where the ans built-in variable was changed into a user variable when loading an external session.
Update the user variables and functions docks after loading an external session if they are visible, as their content might have changed.
Allow NaN to be a valid result for some expressions (user function assignments only). In this case, no result is shown, and the ans variable keeps it value from the latest operation. An empty result string is used for sessions importing/exporting and settings loading/saving.
Proposed another way to save sessions history (check MainWindow::saveSession()) which eases the process and fixes a bug which happens when a user saves a session which contains floating point results and the result format is not decimal: when the user loads this session later, SpeedCrunch is unable to parse non-decimal floating point results from the session file, and thus, it will not show these results in any other result formats (that is, if the user selects a different result format).