Merge pull request #141 from benma/master

Message, xml tag and attribute renames.
Adjust heading levels, add menu metadata, misc. fixes.
Merge pull request #142 from monetas/fix-headings

Adjust heading levels for single-doc output, add menu metadata, misc. fixes.
Rewrap too long lines and fix layout.
Merge pull request #143 from monetas/reflow-parags

Rewrap too long lines and fix layout.
new xml schema for credentials
Merge pull request #144 from mhamrle/credentials_in_xml

new xml schema for credentials
Update notaryMessage.md
Update notaryMessage.md
Add document type `cheque`
Merge pull request #147 from OttoAllmendinger/pr-cheque

Add document type `cheque`
Rename UserID -> NymID, assetContract -> instrumentDefinition.