Add repl sub-command

[amomchilov]

I built this for myself, and found it really useful for faster debugging.

Example usage:

$ bin/prism repl
Prism> 1
@ IntegerNode (location: (1,0)-(1,1))
├── flags: newline, static_literal, decimal
└── value: 1

Prism> 1 +
#<Prism::ParseError @type=:expect_expression_after_operator @message="unexpected end-of-input; expected an expression after the operator" @location=#<Prism::Location @start_offset=3 @length=0 start_line=1> @level=:syntax>
#<Prism::ParseError @type=:unexpected_token_close_context @message="unexpected end-of-input, assuming it is closing the parent top level context" @location=#<Prism::Location @start_offset=3 @length=0 start_line=1> @level=:syntax>
@ CallNode (location: (1,0)-(1,3))
├── flags: newline
├── receiver:
│   @ IntegerNode (location: (1,0)-(1,1))
│   ├── flags: static_literal, decimal
│   └── value: 1
├── call_operator_loc: ∅
├── name: :+
├── message_loc: (1,2)-(1,3) = "+"
├── opening_loc: ∅
├── arguments:
│   @ ArgumentsNode (location: (1,2)-(1,3))
│   ├── flags: ∅
│   └── arguments: (length: 1)
│       └── @ MissingNode (location: (1,2)-(1,3))
│           └── flags: ∅
├── closing_loc: ∅
└── block: ∅

(Well really, it's more a read-parse-print-loop, "RPPL", not "REPL" 😛)

[kddnewton]

Sure!