Add file input support
Use request.url instead of BASE_URL

The issue was only work with "myokoym.net". In this change, rab2pdf
allows running program everywhere.
Merge branch 'sinatra-sapporo-upload-from-file'

Upload from file

Patch by Seiichi Yonezawa. Thanks!
Disable textarea of source if "input file name" is input

Because application give priority to "input file name".