[GH-15] Support for adjacent variable-value syntax

[UrsaDK]

• Support for adjacent variable-value syntax, resolves Double hyphen not handled correctly in some situations #15
• Minor performance improvements

[UrsaDK]

While adding more tests for this change, I realised that this implementation opens up a whole can of worms about how options should be interpreted. For example, when a script that uses : test: tester: for its OPTSPEC is run with --testerror, should it be interpreted as “--test error” or “--tester ror”?

I also disliked the fact that the fixed introduced a for loop that could potentially execute for every option provided, as well as a dependency on the tr and sort commands.

So, I decided to revert adjacent option-value syntax implementation for long options.

Instead, the README will be updated to emphasise that getopts_long supports two syntaxes:

• Short options are compatible with bash’s built-in getopts, supporting both -o value and -ovalue;
• Long options follow GNU-like syntax, supporting only —option value and —option=value definitions.