Issue #81 Work in Progress

* Added convenience methods to CorrugatedIron.StringExtensions to look for `IsUserIntegerKey`, `IsUserBinaryKey`, `IsSystemIntegerKey`, `IsSystemBinaryKey`, and `IsSystemKey`
* Modified `ToIntegerKey` and `ToBinaryKey` to use new detection mechanisms
* removed `magicStrings` List<String> and replaced it two HashSet<String> in `RiakConstants.SystemIndexKeys`: `SystemBinKeys` and `SystemIntKeys`
* Modified `AllKeys` to stop at Unicode 0X10FFFD to avoid sending incorrectly formatted Unicode characters to Riak. For the terrifying side effects, see [Fun with Unicode](http://riak.markmail.org/message/tyypimga2o3xiwih?q=unicode+order:date-backward&page=1#query:unicode%20order%3Adate-backward+page:1+mid:k5y7f7rco554rtor+state:results)
* Added documentation for `AllKeys` and `Keys` explaining the differences