Improve, debug, document tdb
changed lexer tab characters to use an escaped tab (\t)
Fix hash collisions (separate chaining)
Hash table: implement load factor / rehash

Based on suggestion from bitbckt:

I  saw  this  in  my feed, and feel it merits comment. I hope you
don't mind the input.

You'll want to monitor the load factor of the hash table and  re-
hash  the  table  on  insert  when it is exceeded. Otherwise, key
lookup will degrade toward linear time for sets of  keys  with  a
high number of collisions.

The  easiest  way  to  implement the load factor is to maintain a
count of allocated nodes in tvm_htab_t and  divide  that  by  the
bucket count to obtain the load factor. Of course, you'd need the
bucket count (HTAB_SIZE) to be dynamic, too.