Expound on `alias` vs `alias_method` appropriateness

Provides examples of when `alias` is more appropriate than `alias_method` and vice versa, as discussed in issue #377.
I've always capitalized when it's a complete sentence (independent clause) that follows the colon, but I see that CMS, which I usually look to, [doesn't follow that rule](http://www.chicagomanualofstyle.org/qanda/data/faq/topics/Capitalization/faq0008.html); I'll change it. FWIW, it seems to be an [AP vs CMS thing](http://www.apvschicago.com/2011/04/capitalization-after-colons.html).