cli: Add missing copyright header

Can't believe we never had this. o_O
cli: Fix compilation warning

basename() takes a `char *` as its parameter, not a `const char *`.
tests: Drop unused variable
cangjie: Check for errors

We were assuming that everything went just fine and never checking
anything at all.

Baaaaaaad.

Found this with "-Wall -Werror", we should probably try using that more
often! :)
cli: Remove trailing space
Merge pull request #39 from Cangjians/polishing

Polishing