Major character table cleanup:

Major character table cleanup:
* Use ohash(3) rather than a hand-rolled hash table.
* Make the character table static in the chars.c module:
There is no need to pass a pointer around, we most certainly
never want to use two different character tables concurrently.
* No need to keep the characters in a separate file chars.in;
that merely encourages downstream porters to mess with them.
* Sort the characters to agree with the mandoc_chars(7) manual page.
* Specify Unicode codepoints in hex, not decimal (that's the detail
that originally triggered this patch).
No functional change, minus 100 LOC, and i don't see a performance change.