Shrink code block annotation after a comma

[JohnTitor]

The Rust-specific code block annotations like no_run are used in doc testing through doc-comment or similar crates, and other services seem to ignore characters after a comma.
This removes characters from the annotations after a comma.
Since this is additional work, this may affect performance a bit, but from the benchmarks, it looks fine.
Also this allows language-toml class as it's supposed to be used widely.

Small input:

test bench_orig    ... bench:       1,363 ns/iter (+/- 29)
test bench_tweaked ... bench:       1,498 ns/iter (+/- 28)

Large input (about 2k COL):

test bench_orig    ... bench:     634,254 ns/iter (+/- 10,553)
test bench_tweaked ... bench:     636,279 ns/iter (+/- 13,216)

Fixes #1150

r? @jtgeibel

[jtgeibel]

Thanks!

@bors r+

[bors]

📌 Commit 7cba38b has been approved by jtgeibel

[bors]

⌛ Testing commit 7cba38b with merge 4f03f03...

[bors]

☀️ Test successful - checks-travis
Approved by: jtgeibel
Pushing 4f03f03 to master...