Added curved ramp functionality for arches

Example: https://dl.dropboxusercontent.com/u/17850283/challenge.png (made by hand)
Fixed a minor issue with solid generation
Fixed minor issues in arch tool
Fixed, refactored and improved arch brush code
Fixed face creation and tilt angle for arch brush
Changed & fixed how arch brush solids are created
Grammatical changes to arch brush code
Added different split orientations for arch brush
Changed tilt angle boundaries to +-atan(2)

Also allowed floating point values for all inputs apart from number of
sides and changed tilt height adding to use tan instead of sin
Merge remote-tracking branch 'upstream/master'
Changed arch brush to add height per each segment
Added primitive interpolation for arch brush tilt
Added primitive interpolation for arch brush tilt (refactored)
Changed arch brush to use cosine for tilt interp
Grammatical changes to brush controls
Corrected decimal loss on arch brush tilt interp when dealing with an odd number of sides
Merge branch 'master' of https://github.com/KonstantinUb/sledge