Fixed project.

Project was not referencing the system library scripts properly.
Changed how key/values are parsed and processed.
Added keywords to the parser.

Keywords are symbols that start with a colon and evaluate to themselves.
Changed behaviour of 'set!'

'set!' tries to act like 'setf' in Scheme.

Added Test-Set.n to test some of the syntaxes of set!.
Fixed System.n to use the new set! syntax instead of set-index!.
Added NeSet API to do the work with DoSetBang() doing next to nothing.
Removed DoSetIndexBang and 'set-index!' native.
Removed 'set' and 'get' and attaching values to objects.  Symbol properties will take over from that.
Fixed NeGetSubString().
Added new utility NeReplaceSubString().
Added new utility NeReplaceChars().
Added new utility NeAppendLists().
Added new API NeSet().
Upped version to 0.19

New set! and keywords.
Added fold built-in.
Fixed a bug with map and fold.

You could pass a non-pure list to map and fold and make nerd crash.
Added NeLess API to compare atoms.

Replaces IsLess in NeLibCore.
Added kv built-in that constructs a key/value.
Fixed compiler warnings and errors from PC.

Just for master branch for now.