:help command in repl

[ejconlon]

Resolves #1236 . Yields the following output:

$ stack exec dhall repl
Welcome to the Dhall v1.25.0 REPL! Type :help for more information.
⊢ :help
Type any expression to normalize it or use one of the following commands:
:help
    Print help text and describe options
:type EXPRESSION
    Infer the type of an expression
:hash EXPRESSION
    Hash the normalized value of an expression
:let IDENTIFIER = EXPRESSION
    Assign an expression to a variable
:clear
    Clear all bound variables
:load [FILENAME]
    Load bound variables from a file
:save [FILENAME | FILENAME = EXPRESSION]
    Save bound variables or a given expression to a file
:set OPTION
    Set an option. Currently supported: --explain
:unset OPTION
    Unset an option
:quit
    Exit the REPL
⊢

Happy to follow any process or style guidelines. Also happy to change the wording and formatting of the text.

[basile-henry]

This looks great! 🎉
Thank you for your contribution! 😄

[ejconlon]

.history comes from the repl and stack.yaml.lock comes from newer stack versions, I guess.

[basile-henry]

👍

[basile-henry]

👍 (oops, didn't mean to approve twice)