Allow source file to be passed to repl

[openorclose]

Lets you code long stuff in an actual file (like an MCE).

Emulates the Source Academy playground,

where you press run on the left (the file you pass in to the repl)

and eval on the right (the node repl itself).

[coveralls]

Pull Request Test Coverage Report for Build 1880

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 88.906%

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Totals
Change from base Build 1867:	0.0%
Covered Lines:	2188
Relevant Lines:	2397

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💛 - Coveralls

[thomastanck]

LGTM

[anubh-v]

Thanks for this @openorclose, I would really appreciate this feature