This updates some contributing guidelines:

 * Defer to ISSUE_TEMPLATE.md for filing bugs
 * Mention eslint and how to automatically fix style mistakes

* chore(lint): don't allow excess trailing newlines

This enforces that files should not end with blank lines (i.e. more than
one trailing newline). The `eol-last` rule (inherited from airbnb's
config) already enforces that files end in at least one trailing
newline, so adding this rule enforces that it ends in exactly 1.

See https://eslint.org/docs/rules/no-multiple-empty-lines and
https://eslint.org/docs/rules/eol-last for more information.

Inspired by #809.

* add maxBOF

* Remove separate "internal error" from exec

* Fix unknown command error regex

* Add message about command not found regex

* Silence errors while reading files in exec

The stdout and stderr files may never be opened or written to in certain
circumstances. In particular, if the timeout is short enough, the child
node process does not have enough time to start, and the child script
does not execute, so the files are not written to. So, catch errors form
trying to read the files, and ignore them.

* Do not silence errors due to short timeouts

* Simplify test regex for missing command

* Default error code to 1 if not set

Miscellaneous docs/markdown changes. No change to logic.

This fixes #795 (actually, workarounds it.)
For detail, please refer to the issue.