Set version to v0.13.0-pre
Merge pull request #159 from apiaryio/zdne/bump-version

Set version to v0.13.0-pre
Unexpected nodes with keywords will not stop the parsing
Merge pull request #160 from apiaryio/pksunkara/refactor

Unexpected nodes with keywords will not stop the parsing
MSON AST origin. MSON property parser origin.

Conflicts:
	snowcrash.xcodeproj/project.pbxproj
Implicit use of Value<T>::value_type in element value helper
Rename ValueType to DataType for better clarity
Signature parser origin, MSON element parser origin.

Conflicts:
	snowcrash.gyp
	snowcrash.xcodeproj/project.pbxproj
Add checking & warnings to the signature parser

In addition the signature parser is now of standard-parser grade consuming
node iterators and parser data. Also the signature parser now returns any
remaining multiline content.
Support for `-escaped signature variables
Fix project files
SectionTraits origin, singleton sections check origin
MSON element signature parsing completed
Fix wrong copy-pasted test, remove unimplemented property parser tests
Rename Signature Trait "traits" to "specifiers"
Array value parsing
Finished element signature parsing
Finalized MSON property signature parsing
Context for nested sections & descriptions

Add context to nestedSectionType() and isDescriptionNode() to be able
process MSON context-sensitive nested sections
Nested MSON elements parsing