Added "+C"
Change "+C" to "+K" (C is already used as a coefficient in the partial fractions decomposition)
Add "+C" to problem text; remove confusing "+c" in "correct" answer.
Fix subtle perl error "Use of uninitialized value $str"
Added helpLinks for interval notation
Merge remote-tracking branch 'upstream/master'
Merge pull request #85 from paulvojta/master

Bug fixes, mostly adding "+C" and adding helpLinks for interval notation