Implement rb_funcall_with_block

This commit adds `rb_funcall_with_block` (which is available in MRI) to the C
API.
Add specs for rb_funcall_with_block

This commit adds specs for `rb_funcall_with_block`.
Fix empty lines in rb_funcall_with_block spec
Merge pull request #3144 from seanchas116/add-rb-funcall-with-block

Add rb_funcall_with_block