Convert all Singles to Doubles

Except for those that must remain (such as API-related ones).  On modern
processors there is no reason to use singles, as all floating-point
calculations are carried out as doubles anyway.  There may even be a
slight speed increase from this change.
Forcibly limit gaussian blur radius in the IDE
Do not stretch images larger when previewing

If they are small, leave them small
Write my own custom DoEvents for progress bar refreshing

It will only process events related to PhotoDemon - not all other ones.
This should improve performance, while also fixing some re-entry issues
caused by previous use of DoEvents