mature implementation of extensible pattern matching and concerned facilities

1. full featured when syntax: #60, #56
   https://thautwarm.github.io/MLStyle.jl/latest/syntax/when/

2. uncomprehensions(for patterns), need updating docs: #58

     @data S begin S1(x) end
     seq = 1:10
      @match [S1(i) for i in seq] begin
            [S1(i) for i in xs] => xs == seq
            _ => 
      end

3. compilations of string patterns now use isequal instead of `===, need updating docs: #68, #62

4. better error messages: #52

5. QuoteNode patterns, need updating docs : #70

6. README wording improvements: #67, #63