[Issue #5] Generate HTML landing page

[avojak]

Generates an HTML landing page for the update site when accessed through a browser.

Also fixes an issue where POSIX file permissions were used. Clearly that won't work on non-POSIX systems... duh... oops.

[coveralls]

Coverage decreased (-0.4%) to 93.878% when pulling fd39cfc on generate-html into 5b60903 on master.

[coveralls]

Coverage decreased (-0.3%) to 93.97% when pulling 146a413 on generate-html into 5b60903 on master.

[coveralls]

Coverage decreased (-0.03%) to 94.203% when pulling affb25e on generate-html into 5b60903 on master.

[coveralls]

Coverage increased (+4.07%) to 98.305% when pulling b0b8af1 on generate-html into 5b60903 on master.