Fixed #4278: String#underscore with digit

[makenowjust]

Fixed #4278.

It treats digit characters as downcase characters. But in upcase characters it treats like upcase characters. It works fine.

"CSS3".underscore     # => "css3"
"HTTP1.1".underscore  # => "http1.1"
"3.14IsPi".underscore # => "3.14_is_pi"

Thank you.

[makenowjust]

@bew Updated comments in 328d4ce. Thank you.

[makenowjust]

https://travis-ci.org/crystal-lang/crystal/jobs/221621776

Hmm... openssl spec depends on this strange behavior. I think we put _ before V if we need to separate, like NO_SSLV3 to NO_SSL_V3. For example, do you want to convert WMV9 to wm_v9? I say of course 'no'.

NOTE: Original OpenSSL constant name is NO_SSLv3, not NO_SSLV3. v is just lower case letter. It is important thing that we don't respect original constant name already.

[asterite]

Let's rename openssl constants to match this new behaviour.

Since we are fixing this, what happens if you pass other characters like some of !@#$%^&*() to underscore? I'd include some tests for those edge cases too and make sure they behave like in Ruby's ActiveSupport.

[makenowjust]

@asterite Apologize for delay. I renamed OpenSSL constants for changes and updated this branch.

I know ActiveSupport's String#underscore converts "::" to "/" for Rails convention. However I think it is for Rails reason, so I don't implement it for now.

[akzhan]

I prefer to use ActiveSupport compatible behavior when it's possible and have no drawbacks.

[makenowjust]

I'm sure String#underscore is bad naming if it converts "::" to "/".

[makenowjust]

@asterite ping

[mverzilli]

Thank you @makenowjust !!!

[makenowjust]

@mverzilli Can you close #4281?