Improved web interface, code cleanup and script support

• Add option to run arbitrary scripts: In addition to XSD/XSLT, arbitrary executable scripts can be placed
  in ./script/validate and ./script/transform/, written in Python, bash or compiled C code.
• Validation: hocr against hocr-check from tmbdev/hocr-tools
• Web interface: Download button for transformation results
• Web interface: Support file uploads for transformation and validation
• Enable ALTO/hocr to plain text transformations
• Code cleanup of the shared shell script library

More details: v0.1.0...v0.2.0