Various fixes and integration tests

[raszi]

Fixes

• ttl-insulate had a malformed let, so it never bound s and never saw string or comment state.
• The idle timer re-indented the line under point in every ttl-mode buffer. Removed it and its two options.
• Blank-node predicates and objects after a comma now indent two levels, so they clear the predicate column.
• A # at the start of the buffer now opens a comment.
• Removed a duplicate ttl-electric-comma binding.
• Enabled lexical-binding, replaced point-at-eol with line-end-position, and cleared the byte-compile warnings.

Tooling

• Easkfile and a Makefile with lint, test, and clean.
• GitHub Actions CI on Emacs 26.1, 28.2, 29.4, and 30.2: compile, package-lint, Buttercup.
• Buttercup tests for indentation, comment syntax, blank nodes, strings, electric dot, and highlighting. Some cover upstream closed issues.
• Package headers (version 0.2.0, Package-Requires: emacs 26.1) and a .gitignore for build output.

The file also moved from tabs to spaces, so part of the diff is whitespace only.