table: Fix comment

The previous one didn't make a lot of sense, now that I read it again
after some time.
table: Add fullwidth numbers

An early tester of IBus Cangjie just asked me if we could do this, and
it seems like a reasonable improvement.
data: Make the frequency per code, rather than per character

This will allow us to have a more fine-grained control over the results
we display to the user for characters which have multiple codes.

This changes the database model, but fortunately it doesn't break the
libcangjie2 API at all.
dbbuilder: Allow multiple lines for one character in the source table

This will make it possible to define different per-code frequencies for
a given character.
table: Have two frequencies for 氐

The 氐 character has 2 Cangjie codes in our data: 'hpm' and 'hvpi'.

However, depending on the reference sources (dictionaries, CBF's
website, the chinesecj.com forum,...), we can find either only 'hpm',
or both.

That's all a bit confusing...

Doing some tests with Cangjie users, they only knew about the 'hpm'
code, never the 'hvpi' one (although once told about it, they were
usually able to understand how to decompose 氐 in 'hvpi').

That tells me that 'hpm' is absolutely necessary, but not 'hvpi'.

Unfortunately, 'hvpi' is actually causing us trouble, as Quick users
don't expect to see 氐 as the third result when typing 'hi'. In fact,
they don't expect it at all when typing 'hi', only when typing 'hm'.

The way out is to set the frequency to 0 for this character when called
by the 'hvpi' code, so that it appears way low in the list.

That should please Quick users.