eval zoom: bugfix
Merge remote-tracking branch 'origin/plpython' into plpython
eval line merge: re-implement in plpython + tests
Compile Condition(s): drop parameter prefix
Compile Properties: bugfix
Eval Test Function: add to_float() function
re-implement more eval functions

- geom functions: buffer, line, line_interpolate_point, line_length,
  line_locate_point, line_part
- color functions: deluma, lighten
- more tests for metric
Eval Test Function: make sure return value is a string
eval functions: return float values with highest precision
re-implement more eval functions

- natsort, random, switch, sqrt
- geom: rotate, translate