v3.0.0

Bump! 💃🏻

Diff: v2.2.3...v3.0.0

Changes:

• upgraded to mPDF v6+
• travis: tests against php7
• composer: required php5.4+
• PdfResponse: introduced PdfResponse::ZOOM_* and PdfResponse::LAYOUT_* constants
• PdfResponse refactored - added property accessors with validation for most of the fields
• removed (deprecated) ITemplate support from Nette <2.2