Use String#start_with? to detect leading special character

[elebow]

This change uses Ruby's built-in String#start_with?, which is implemented entirely in C (in MRI, anyway) and faster than the current implementation. String#start_with? is available in all versions of Ruby that CSVSafe supports.

Benchmarks show a 4.1% speed improvement in line generation.

require "benchmark"

Benchmark.bmbm do |bm_out|
	bm_out.report { 5_000_000.times { CSVSafe.generate_line(["|yes", "no"]) } }
end

Legacy code:

       user     system      total        real
  92.012501   0.246394  92.258895 ( 92.277018)

This branch:

       user     system      total        real
  88.270658   0.248487  88.519145 ( 88.541700)

The #starts_with_special_character? method itself is between 20.9% and 28.2% faster, using a similar benchmark.

I was unable to find any cases where this branch is slower.

[zvory]

thank you

[zvory]

rolled out in #14 and released to rubygems.