Root now supported
setExponent(Expression) fix
Exponential symbolic combination supported
#72 partially fix (ex. 1, 3, 4, and 5), #84 #85 #86 #87 fix
power -> symbol fix
Variable powers are more secure and easier to maintain
#72 fix ex. 2
Bounding Box caching

Signed-off-by: bvanr <henkibrij@hotmail.com>
Merge remote-tracking branch 'folkert/work' into work
Merge remote-tracking branch 'bas/basbranch2' into work
The cache of an expression is now properly invalidated

Signed-off-by: Mark Kamsma <mark@markkamsma.nl>