Wrong default encoding for loading code snippets

[denisdefreyne]

Steps to reproduce

1. Set environment in encoding to ASCII
2. Add some UTF-8 content to lib/ (e.g. 🔥 = 'hot')
3. Compile site

Expected behavior

No crash.

Code snippets are loaded with the explicitly stated encoding at the top of the file (e.g. # encoding: utf-8), or UTF-8 if no encoding is specified.

Actual behavior

Crash.

SyntaxError: lib/hi.rb:1: invalid multibyte char (US-ASCII)

Code snippets are loaded with the encoding defined in the environment.

Details

This also applies to Rules, Checks, and commands defined in commands/.

An initial step would be to interpret the contents as UTF-8 (which Ruby defaults to anyway), but a better approach would be to infer the encoding from the initial line, looking for encoding/coding.

CC @josh-