This fixes #3248

• Set the file name in error message
• Parse whole file at once so correct lines numbers are given in errors
• Don't fail on empty lines, whitespace, etc

To ensure line numbers are given on errors, I made a new parser that only parses import statements, instead of parsing all kinds of commands and rejecting them after the line numbers are forgotten.

Since the whole file is parsed all at once, it no longer makes sense to interleave printing, parsing, and executing line-by-line. So I've printed the whole contents verbatim before executing all the imports (assuming the file parsed).

Example:

$ cat .purs-repl
import Prelude
:help

$ pulp repl
PSCi, version 0.11.7
Type :? for help

"/home/guest-user/example/.purs-repl" (line 2, column 1):
unexpected :
expecting "import" or end of input
The .purs-repl file only supports import declarations