implement speedups with rust v2

[carsonburr]

pip install -e . in a virtualenv should build src/markupsafe/_rust_speedups.???.so, assuming you have Rust installed.

python bench.py to run all benchmarks, rust included. Here's the results on my machine:

$ python bench.py

short escape native: Mean +- std dev: 656 ns +- 12 ns
short escape speedups: Mean +- std dev: 417 ns +- 7 ns
short escape rust_speedups: Mean +- std dev: 522 ns +- 15 ns

long escape native: Mean +- std dev: 17.3 us +- 0.2 us
long escape speedups: Mean +- std dev: 7.79 us +- 0.14 us
long escape rust_speedups: Mean +- std dev: 6.71 us +- 0.08 us

short plain native: Mean +- std dev: 505 ns +- 9 ns
short plain speedups: Mean +- std dev: 349 ns +- 5 ns
short plain rust_speedups: Mean +- std dev: 401 ns +- 4 ns

long plain native: Mean +- std dev: 17.2 us +- 0.1 us
long plain speedups: Mean +- std dev: 7.77 us +- 0.10 us
long plain rust_speedups: Mean +- std dev: 6.73 us +- 0.15 us

long suffix native: Mean +- std dev: 134 us +- 1 us
long suffix speedups: Mean +- std dev: 131 us +- 1 us
long suffix rust_speedups: Mean +- std dev: 58.3 us +- 1.2 us

[davidism]

I'll have to run it on my machine for an exact comparison, but those are some good performance numbers compared to the C for the long benchmarks.