Squashed 'Raven.Voron/' changes from 9b3f54d..facd6bd

facd6bd Making sure that we properly dispose the streams that were sent to WriteBatch
483f622 Minor optimization
137a2df Adding support for explicit snapshots in the API
1921fca Null tree name means the root
f85d222 Better name for tx merging writer Added sync version of the WriteAsync method

git-subtree-dir: Raven.Voron
git-subtree-split: facd6bd1e83dd6b8503b1d9f93104ea6b47d879b
Merge commit '5d7f01604c114ec1d5fd1c20768368e0b1e3273d' into 2.5-voron

Conflicts:
	Raven.Voron/Voron/Impl/TransactionMergingWriter.cs
	Raven.Voron/Voron/Impl/WriteBatch.cs
	Raven.Voron/Voron/Voron.csproj