* Update unitype lib which improves subsetting
* Add text extraction check to creator font subsetting example
Helps ensure ToUnicode map is set correctly.
* Clean up import
* Fix spelling
* Subsetting of TrueType CID fonts using unitype
* Simplify call to SubsetRegistered so can be done right after loading font via creator finalizer
* Add an EnableFontSubsetting function on the creator to simplify font subsetting for creator users
* Add render package
* Add text state
* Add more text operators
* Remove unnecessary files
* Add text font
* Add custom text render method
* Improve text rendering method
* Rename text state methods
* Refactor and document context interface
* Refact text begin/end operators
* Fix graphics state transformations
* Keep original font when doing font substitution
* Take page cropbox into account
* Revert to substitution font if original font measurement is 0
* Add font substitution package
* Implement addition transform.Point methods
* Use transform.Point in the image context package
* Remove unneeded functionality from the render image package
* Fix golint notices in the image rendering package
* Fix go vet notices in the render package
* Fix golint notices in the top-level render package
* Improve render context package documentation
* Document context text state struct.
* Document context text font struct.
* Minor logging improvements
* Add license disclaimer to the render package files
* Avoid using package aliases where possible
* Change style of section comments
* Adapt render package import style to follow the developer guide
* Improve documentation for the internal matrix implementation
* Update render package dependency versions
* Apply crop box post render
* Account for offseted media boxes
* Improve metrics of rendered characters
* Fix text matrix translation
* Change priority of fonts used for measuring rendered characters
* Skip invalid m and l operators on image rendering
* Small fix for v operator
* Fix rendered characters spacing issues
* Refactor naming of internal render packages
