Create a better benchmark suite

[jdkato]

As mentioned in #26, one of the goals of our test suite is to include better profiling information. Vale is pretty fast at the moment (especially when compared to other prose linters), and it'd be nice to be able to measure how changes impact this without having to profile the entire application. For starters, I think we should do this at the package level:

• core
• lint
• check
• rule
• ui

[jdkato]

On every commit, we now check our linting speed against the last tagged release. For example,

BenchmarkLintRST-2     1366062472     1361922518     -0.30%
BenchmarkLintMD-2      1363626049     1360176779     -0.25%
BenchmarkLintRST-2     1376474766     1386861581     +0.75%
BenchmarkLintMD-2      1370244341     1357384946     -0.94%
BenchmarkLintRST-2     1428971289     1377332166     -3.61%
BenchmarkLintMD-2      1354160155     1361084509     +0.51%
BenchmarkLintRST-2     1394186877     1382955863     -0.81%
BenchmarkLintMD-2      1354047104     1373768666     +1.46%
BenchmarkLintRST-2     1377752403     1388631529     +0.79%
BenchmarkLintMD-2      1363557789     1382063938     +1.36%
name       old time/op  new time/op  delta
LintRST-2   1.39s ± 3%   1.38s ± 1%   ~     (p=0.841 n=5+5)
LintMD-2    1.36s ± 1%   1.37s ± 1%   ~     (p=0.548 n=5+5)