Content-Security-Policy, etc

Changes:

• Avoid fall through in the keyword transform, thanks to @lrowe in #164
• Replace the keyword transform with a Map, to avoid triggering unsafe-eval Content-Security-Policy warnings, thanks to @jsharkey13 in #173
• Fix a bug in reset() relating to queuedText, thanks to @hikerpig in #169
• Improve error reporting and add additional context lines, thanks to @airportyh in #129

Documentation tweaks:

• Correct states example to use pop: 1, thanks to @evanpurkhiser in #140
• Replace itt example with modern js example, thanks to @AlansCodeLog in #147

Full Changelog: v0.5.1...v0.5.2