C++ bindings

[emuell]

• added c++ bindings/FFI layer and a relay, as used by Renoise
• added descriptions on how to use your own version of patterns in Renoise
• updated global README to explain monorepo structure

@unlessgames could you have a quick look at this, if that makes sense - and reads okay?
It's yet another sub-project, but I like mono repos, so I've at least added an overview of the sub projects in the README.

Also, note 'Using a Custom pattrns Library in Renoise', which I wanted to document anyway, as well as in relation to #73.

[github-actions]

Benchmark for 1690f37

Click to view benchmark

Test	Base	PR	%
Cycle/Generate	48.7±0.63µs	48.2±0.65µs	-1.03%
Cycle/Parse	373.0±7.46µs	376.0±11.13µs	+0.80%
Rust Phrase/Clone	434.1±5.82ns	431.7±6.14ns	-0.55%
Rust Phrase/Create	74.4±1.31µs	75.3±0.95µs	+1.21%
Rust Phrase/Run	628.7±6.45µs	644.3±4.05µs	+2.48%
Rust Phrase/Seek	141.5±262.36µs	137.7±255.89µs	-2.69%
Scripted Phrase/Clone	658.7±6.06ns	650.9±6.21ns	-1.18%
Scripted Phrase/Create	943.3±21.55µs	960.4±9.96µs	+1.81%
Scripted Phrase/Run	1683.6±15.36µs	1687.9±16.65µs	+0.26%
Scripted Phrase/Seek	222.2±449.11µs	219.6±445.83µs	-1.17%

[unlessgames]

I have tried building and copying the libpattrns.so on linux but Renoise crashes with

Renoise LOG> Player: Loading pattrns rhythm library from: '/home/user/.config/Renoise/V3.5.1/libpattrns.so'
Renoise LOG> Exception: failed to resolve pattrns function: 'new_phrase'.
Renoise LOG> Error Message: failed to resolve pattrns function: 'new_phrase'.
>> XMessage: failed to resolve pattrns function: 'new_phrase'.

[emuell]

Wanted to get rid of a few unused functions (the phrase API). Those functions never have been used.

Added stubs for them and will get rid of them properly with the next Renoise update.

[github-actions]

Benchmark for 45dfdfe

Click to view benchmark

Test	Base	PR	%
Cycle/Generate	48.9±0.90µs	48.7±0.32µs	-0.41%
Cycle/Parse	379.4±5.50µs	376.6±4.78µs	-0.74%
Rust Phrase/Clone	440.6±6.97ns	433.6±7.80ns	-1.59%
Rust Phrase/Create	76.4±0.96µs	75.8±0.86µs	-0.79%
Rust Phrase/Run	632.2±4.30µs	638.9±3.35µs	+1.06%
Rust Phrase/Seek	134.6±249.73µs	135.3±250.26µs	+0.52%
Scripted Phrase/Clone	649.6±6.03ns	656.4±24.59ns	+1.05%
Scripted Phrase/Create	959.2±17.15µs	943.8±9.88µs	-1.61%
Scripted Phrase/Run	1679.6±6.48µs	1676.9±44.97µs	-0.16%
Scripted Phrase/Seek	220.2±446.43µs	218.5±443.39µs	-0.77%

[emuell]

Probably ffi or bindings would be a better folder sub project name here? cbindgen currently is generating a c++ header, but it could also generate a plain C header instead or additionally...

[unlessgames]

Can't really comment on the implementation aspect as this is unfamiliar territory for me, but the instructions are easy to follow and the build now works fine on Linux.

I agree that ffi might be a better name, especially if this will be extended beyond c++ later.

[emuell]

Had renamed that to bindings already. I think that's fine too.

[github-actions]

Benchmark for 8dc155f

Click to view benchmark

Test	Base	PR	%
Cycle/Generate	49.0±0.33µs	48.2±0.40µs	-1.63%
Cycle/Parse	371.7±27.12µs	381.3±7.56µs	+2.58%
Rust Phrase/Clone	434.7±6.13ns	432.7±4.07ns	-0.46%
Rust Phrase/Create	74.6±1.16µs	76.2±1.20µs	+2.14%
Rust Phrase/Run	626.7±5.65µs	633.7±5.95µs	+1.12%
Rust Phrase/Seek	137.5±257.34µs	135.7±251.57µs	-1.31%
Scripted Phrase/Clone	669.3±5.04ns	652.7±5.89ns	-2.48%
Scripted Phrase/Create	957.9±9.49µs	952.8±30.01µs	-0.53%
Scripted Phrase/Run	1676.8±10.97µs	1659.5±9.82µs	-1.03%
Scripted Phrase/Seek	220.3±445.67µs	218.1±441.08µs	-1.00%