[rebased] Use ragel-bitmap for less memory

[ahorek]

this is a rebased version of #1343

it significantly reduces resident memory by -39MB
but there are downsides:

performance
-9% mri 3.4.0 (dev)
-1% mri 3.4.0+yjit
-10% jruby
0% jruby+indy
-10% truffleruby
and +6% runtime allocations

however, it's a micro-benchmark and differences are marginal, so it's unlikely to be a bottleneck in a real application.

[jrafanie]

@ahorek can you share your benchmark script? I'd like to test in my project but am not sure if the parsers are eager required via require 'mail' or if I need to do something different to demonstrate the benefits and tradeoffs of this change.

Thanks!

[ahorek]

nothing special

file = File.binread("email.eml")
Mail.new(file).to_s

https://github.com/evanphx/benchmark-ips
https://github.com/zombocom/derailed_benchmarks