Rename the table LICENSE file

It makes no sense to call this file LICENSE, when the Public Domain is
an absence of license.

COPYING is widely used in Free Software projects, so that seems like a
good candidate for a name.

However, to avoid conflicting with the libcangjie COPYING, let's suffix
this one with .tables.
Greatly simplify the handling of tables

The names of the source tables were completely inexpressive and
confusing.

Renaming them to the same naming convention as the generated databases
also simplifies a lot the build system, as can be seen by all the lines
removed from Makefile.am and the unit test.
Add a README.tables

This should make it clearer what these files are.
Remove some old unused comments
Export the two helper functions to a util module

This will be helpful later on, to reuse them elsewhere.
Move the dbbuilder sources

Splitting it into its own tools/subfolder doesn't bring us anything, and
it actually makes things harder for the future.
Ignore empty and commented lines when building the tables
Add some Hong Kong-specific characters

Hong Kong people use almost exclusively Traditional Chinese.

However, they use some characters which are not in our current TC
tables, because they are either coming from Simplified Chinese, or from
very old Chinese language.

These should be available readily to Hong Kong users, and as such they
should be in our TC tables.

Note that I didn't invent the input code from thin air, I reused the
ones existing in the CC tables.