Add opal backtrace for compilation errors

[elia]

Adds the location of the error inside the opal file that's being compiled for a better user experience.

Example:

opal:elia/opal-backtrace-for-compilation-errors ⤑ echo '1                                                                              ~/C/opal
                                                  2
                                                  3
                                                  4
                                                  5
                                                  def {}' > tmp/prova.rb
opal:elia/opal-backtrace-for-compilation-errors ⤑ bin/opal tmp/prova.rb                                                                ~/C/opal
tmp/prova.rb:6:5: error: unexpected token tLCURLY
tmp/prova.rb:6: def {}
tmp/prova.rb:6:     ^ 
Traceback (most recent call last):
	22: from bin/opal:4:in `<main>'
	21: from bin/opal:4:in `load'
	20: from /Users/elia/Code/opal/exe/opal:24:in `<top (required)>'
	19: from /Users/elia/Code/opal/lib/opal/cli.rb:66:in `run'
	18: from /Users/elia/Code/opal/lib/opal/cli.rb:78:in `builder'
	17: from /Users/elia/Code/opal/lib/opal/cli.rb:107:in `create_builder'
	16: from /Users/elia/Code/opal/lib/opal/cli.rb:146:in `evals_or_file'
	15: from /Users/elia/Code/opal/lib/opal/cli.rb:107:in `block in create_builder'
	14: from /Users/elia/Code/opal/lib/opal/builder.rb:95:in `build_str'
	13: from /Users/elia/Code/opal/lib/opal/builder_processors.rb:94:in `requires'
	12: from /Users/elia/Code/opal/lib/opal/builder_processors.rb:84:in `compiled'
	11: from /Users/elia/Code/opal/lib/opal/compiler.rb:173:in `compile'
	10: from /Users/elia/Code/opal/lib/opal/compiler.rb:187:in `parse'
	 9: from /Users/elia/Code/opal/lib/opal/compiler.rb:232:in `re_raise_with_location'
	 8: from /Users/elia/Code/opal/lib/opal/compiler.rb:187:in `block in parse'
	 7: from /Users/elia/.rvm/rubies/ruby-2.5.1/lib/ruby/gems/2.5.0/gems/parser-2.5.1.0/lib/parser/base.rb:214:in `tokenize'
	 6: from /Users/elia/Code/opal/lib/opal/parser/default_config.rb:32:in `parse'
	 5: from /Users/elia/.rvm/rubies/ruby-2.5.1/lib/ruby/gems/2.5.0/gems/parser-2.5.1.0/lib/parser/base.rb:167:in `parse'
	 4: from /Users/elia/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/racc/parser.rb:259:in `do_parse'
	 3: from /Users/elia/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/racc/parser.rb:259:in `_racc_do_parse_c'
	 2: from /Users/elia/.rvm/rubies/ruby-2.5.1/lib/ruby/gems/2.5.0/gems/parser-2.5.1.0/lib/parser/base.rb:262:in `on_error'
	 1: from /Users/elia/.rvm/rubies/ruby-2.5.1/lib/ruby/gems/2.5.0/gems/parser-2.5.1.0/lib/parser/diagnostic/engine.rb:73:in `process'
tmp/prova.rb:6:in `def {}': unexpected token tLCURLY (Opal::SyntaxError)
opal:elia/opal-backtrace-for-compilation-errors ⤑