cleanup
template: specify content type for scripts and stylesheets

While these usually are JavaScript and CSS, it is good practice to
make that explicit.
template: do not use http-equiv="X-UA-Compatible" with "chrome=1"

This is meant to force the Chrome Frame plugin, and is deprecatd.
template: include MathJax by default
update.g: output homepage URLs for package dependencies
template: add hyperlinks to deps, and also list suggested deps
Add link to issue tracker
Only link to issue tracker if it is active
Update config for latest jekyll
Add .md extension to _README, add symlink README.md to it
Tweak README further
Improve README
Some more tweaks
Link to ReleaseTools
Add license info
Add contact info
Add list of packages using GitHubPagesForGAP

Closes #2
Fix typo in README
Tweak stylesheet to not cut off package name
Display current package version in side bar