Make rb_funcall3 disallow private methods
Add specs for rb_funcall3
Enumerable#sort works even if #to_a returns a frozen Array

Ruby's documentation on Enumerable#to_a does not suggest that the returned
Array must be mutable (only that it must contain the items in the Enumerable).
In fact, Array#to_a itself can return a frozen Array. Therefore, it is better
to account for Enumerables which return a frozen Array from #to_a.
Add spec ensuring Enumerable#sort works even if #to_a returns a frozen Array
Specs and implementation of Enumerable#to_h, Array#to_h
Merge pull request #3109 from pd/enumerable-to_h

Specs and implementation of Enumerable#to_h, Array#to_h
Merge pull request #3104 from alexdowad/enumerable_sort_with_frozen_array

Enumerable#sort works even if #to_a returns a frozen Array
Merge pull request #3096 from seanchas116/rb_funcall3-public-only

Make rb_funcall3 call only public methods
Remove 'register' keyword from st.h in C API

'register' keyword is meaningless in modern compilers and it causes
deprecation warnings in C++11 compilers.
Merge pull request #3111 from seanchas116/remove-register-from-st-h

Remove 'register' keyword from st.h in C API
Format README in Markdown
Clean-up line breaks
Make LICENSE a link
Create links to other repo resources
Syntax highlight command line examples
Add Table of Contents
Clean-up; Add punctuation
Add link to Rails
Tidy up 'Keyword arguments' link
Format CONTRIBUTING in Markdown