Modify unit test for the new API change

Modified the cangjie_char_new() statments to add simpchar.
Also added the assertion of simpchar field.

Should fix the error in Travis CI building process.

Changes from ee038be to this commit should be sufficient to
resolve #40.
Update documentations to the changed API

The function cangjie_char_new() and the struct CangjieChar have
been changed. This commit updated the relevant documentations for
these changes.