internal/ini: add support for ini parser

[xibz]

New PR since rebasing the old one was intense.

ini parser uses an LL(1) parser to generate a list of sections from an ini file or bytes.
This change will get rid of a dependency and below is the benchmark data for this change:

BenchmarkINIParser-4              100000             15926 ns/op           13312 B/op         45 allocs/op
BenchmarkGoINIParser-4            200000              7393 ns/op            8528 B/op         65 allocs/op

See #2024 for more information.

[jasdel]

also should update the go.mod file dependencies.

[emmanuel]

Great perf. But the behavior changed without warning: #2281

(To be clear, perhaps more than one space between LHS tokens and equals sign was never intended to be supported. Whatever the intent; it used to work, and now it doesn't.)