Squashed 'Raven.Voron/' changes from 0030c1b..01c4616

01c4616 minor fixes
a981196 added root tree name to constants
0c62c2e minor
3261263 fixed in TransactionMergingWriter (better batch group building, preventing splitting writes when not necessary)
c54e9f5 slightly faster operation detection inside WriteBatch
7897645 allow empty values
bd1373b added *.DotSettings to ignore
079cba3 fixed a problem with Tree::MultiAdd() --> adding multiple times the same key/val pair
8391373 fix of Page::Search bug (that was rolled back for unknown reason)
991e8a2 Minor optimizations
2af3c22 Removing unused (and wrong) method
f564c5d changed Tree::ReadVersion() and Tree::GetDataSize() methods to return info _only_ if specified key exists

git-subtree-dir: Raven.Voron
git-subtree-split: 01c46165406d7c69f797a04b812296011c005cd2
Merge commit 'c03ae09864b3b57586ab5ecc85dd40d997dcdab8' into 2.5-voron

Conflicts:
	Raven.Voron/.gitignore
	Raven.Voron/Voron.Tests/MultiValueTree.cs
	Raven.Voron/Voron/Impl/Constants.cs
	Raven.Voron/Voron/Impl/SnapshotReader.cs
	Raven.Voron/Voron/Impl/TransactionMergingWriter.cs
	Raven.Voron/Voron/Impl/WriteBatch.cs
	Raven.Voron/Voron/StorageEnvironment.cs
	Raven.Voron/Voron/Trees/Page.cs
	Raven.Voron/Voron/Trees/Tree.cs