Added support for here-documents (<<"EOT", <<'EOT')
Added the equality operator for hashes (==) which returns true if two hashes holds the same keys;
Added the extra-equality operator for hashes (===) which returns true if two hashes holds the keys and values;
Fixed the defined-or (\\) operator. Now, it will not execute its argument if the variable is defined;
Added a new sidef script: scripts/cnp.sf (which implements the here-doc feature)