Moves many methods previously provided by implicit conversions directly onto the classes
for better discoverability, especially with scaladoc.
1. Initialize now allowed in more places. Minor renamings in Initialize to avoid conflicts
a. map -> apply
b. get -> evaluate
2. Identity on Scoped* is deprecated- it is now redundant
3. Can now use += and <+= for String, Int, Long, Double settings.
There may be some problematic corner cases in inference, especially with +=, ++, <+=, <++=
4. Some classes with a scoped: ScopedKey[T] method now have scopedKey: ScopedKey[T] instead.
5. The implicit conversion to ScopedKey[T] is now deprecated. Use the scopedKey method.
6. :== and ::= are now private[sbt] to better reflect that they were internal use only.
Mark Harrah