Merge pull request #16 from krtx/master

Add account management
Fixed a bug.
reject -> reject!
Merge pull request #21 from krtx/master

Fixed a bug.
Use zip library to compress files and patterns to specify files
Merge pull request #22 from OKU1987/oku/gem

Use zip library to compress files and patterns to specify files
Change the ways to tokenize and to group exercises

Only exercises which share the same prefix have parent-child relations
Merge pull request #17 from OKU1987/oku/grouping

Change the ways to tokenize and group exercises
Validates the input in register.cgi.