[#5] Add 'repl' command to morley

Description

Adds a simple REPL for running Morley instructions. Right now a command 'repl' is added to morley executable morley-client morley executable. The REPL starts with an empty stack. Instructions can be entered, possibly multiple ones separated by semicolons. After execution, the modified stack is printed. Use ":help" to see the available commands after starting the REPL.

Related issue(s)

Resolves #5 (closed)

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