Compile fix (nw)
Allow sound output if 8253 is never programmed, i.e. all output is done by modulating speaker output line.
Merge pull request #35 from shattered/_dcd0ca6

Allow sound output if 8253 is never programmed, i.e. all output is done ...
upd7810: fix bug introduced in extended timer simplification
upd7810: ECNT clear control happens after capture control
upd7810: fix and export timer/event counter output

The timer/event counter outputs (CO0 and CO1) are set differently when
EOM changes and when a timer update occurs. Most EOM values are
cleared on use. The document at [0] is confusing regarding these bits.
An older document [1], easier to understand, was used instead.

[0] NEC Electronics User's Manual, April 1987
[1] NEC uCOM-87AD Family 8-Bit Microcomputers uPD78C1X Users Manual