Adding puzzler 'Oddly Enough'

Based on a suggestion by @axel22 (Aleksandar Prokopec)
'&' -> '&amp;' in puzzler sources
Harmonizing references to 'Stack Overflow'
Harmonizing references to 'scala-language mailing list'
Harmonizing description of runtime exceptions and compiler errors

* "throws a runtime exception"
* "fails to compile"
Using the updated Scala favicon
Moving 'What Were You Expecting?' to the archive

Fixed in 2.11.2 - thanks to @varju for spotting that!
Adding a 'Made obsolete by' item to the puzzler intro for archived puzzlers

Based on a discussion with @xhudik
Adding 'Made obsolete by' to 'What Were You Expecting?'