- Loyc.Essentials: reorganized code, adding Collections/Adapters and Strings subfolders

- Loyc.Essentials: added support for Fails property to TestAttribute
- LEL: Added macros: unroll(x in (...)) {...}, null dot (a?.b), concat_id a.k.a. ##, x ??= y, A := B, B =: A
- EC#: changed x?.y?.z to parse as x?.(y?.z), barely started LINQ parsing
- Loyc.Syntax: added LNode.Select(), LNode.ReplaceRecursive(), and static methods that inherit Range and Style from a "prototype" node. LNode now implements INegListSource<LNode>
Merge branch 'master' of https://github.com/qwertie/Loyc

Conflicts:
	Src/LEL/Prelude.cs
	Src/Loyc.Essentials/Collections/ExtensionMethods/LCExtensions.cs
	Src/Loyc.Essentials/Loyc.Essentials.csproj
	Src/Loyc.Utilities/Loyc.Utilities.csproj
Removed Loyc.NET4.sln (now combining .NET 3.5 and 4.0 targets in Loyc.sln)