Toys: Fix parameter name of the text in text_kwargs.

See merge request !52

Used fixed_parameters in FMM kernels to avoid temp shape fallback warnings.

See merge request !51

warnings.

Scale expansion coefficients with expansion radius

See merge request !46

Add full control over expansion text labels. Closes #22.

Closes #22

See merge request !50

get_common_arg_candidates(): Avoid calling sort().

See merge request !49

test_dont_cse_subs() :Avoid creating explicit Subs nodes.

See merge request !48

At least on my branch of SymEngine (v0.3.0), this test fails because
it greedily evaluates the Subs nodes.

This code is the hot spot for CSE and so it is better to avoid any
needlessly expensive function calls.

Remove derivatives in translation operators

See merge request !47