Merge branch 'upstream/master'
Staircase now using better interface consisting of struct of function handles when in v2 mode. When staircase is created with original call (no inputs), nothing has changed for the user. Internals are reworked though...
construct lookup table so that we evaluate psychometric function only once for each probe level
set_psychometric_func immediately checks if requested psychometric function is valid and creates function handle (so we get rid of a switch in the inner loop)
made sure precomputeLookup exits early when nothing todo
now have useer setting to force lookup table use on or off. if not set, lookup table is created if it isn't too large
now have a compressed version of the lookup table if stepsize of probeset and aset are the same
Merge pull request #182 from dcnieho/master

Staircase update by Diederick:

Some updates to staircase internals. Cleaner and faster.
Also new API that is better (but default is the legacy API,
so users won't notice this upgrade)