Matrix: flatten resampler and test on refined geometry

See merge request !111

Refactor performance modeling code.

See merge request mattwala/pytential!3

This splits assemble_performance_model() into a PerformanceModel class
and TranslationCostModel class. This also breaks the individual
processing procedures up into methods.

Address some fixmes in the code

See merge request inducer/pytential!109

Move performance model into separate file

See merge request mattwala/pytential!2

Faster ci

See merge request mattwala/pytential!1

algorithm meets a strict tolerance.

Div s test and fixes

See merge request !107

Fix test_matrix

See merge request !106