455 kHz projector for YS2000

Revision register 1813 (hex)

Set default envelope definition (tukey) to reflect a Tukey value of 0
Note 1713 was built incorrectly with incorrect default frequency of 200KHz and rev register correctly reflected this error (1710)

Mods in rev 1713

Allow weighting of the pulses on per ping basis to allow cap bank to be left charged
Several files are involved in this modification

Note revision 1613 had a bug and was never released

Rest is from previous revision

Overall improvement of tukey window functionality and decreasing fm sweeps

Modified single_ifpwm.v to allow for 

1)	proper ramp down for non zero tukey parameter (added additional counters etc)
2)	changed logic to calculate the events one zero crossing ahead and reintroduced a separate counter to set the events
3)	adjusted timing so that the envelope, chirprate line up correctly in phase 
4)	sign extend chiprate (per Anders) to allow for decreasing fm sweeps
5)	fix vanishing pulses at non zero tukey parameter value (occurs when envelope rate larger than zero cross period)
6)	fix vanishing pulses at tukey parameter = 1 (no slop between ramup and rampdown)

Revision register 1513 (hex)

Bin file is stx455K_1513.bin

Note fixes 1-4 were in rev 1313 (hex)
Fixes 5-6 is added to rev 1513 (hex) 02/19/08
