Added initial implementation for REPL examples

[anubhav7495]

#59

[anubhav7495]

[anubhav7495]

[anubhav7495]

For having all es2015 page examples on REPL

-- Moved content of learn-es2015.md except the YAML front matter in to _includes folder as es2015.md. -- included the es2015.md in learn-es2015.md for it to work correctly. -- included the es2015.md file in REPL.html in a hidden <div>. -- use the hidden <div> data for populating options for examples <select>.

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