Update addon homepage

[spiralofhope]

http://bugs.code.downthemall.net/trac/wiki/AntiContainer => https://github.com/downthemall/anticontainer

[spiralx]

There are also some broken and outdated links on the Writing Plugins page:

• GitHub should link to http://github.com/downthemall/anticontainer/tree/master/plugins/
• replace() documentation should link to https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace
• RegExp documentation should link to https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp

The latter two links are currently redirected to the correct URLs, but that could change.

[nmaier]

fixed