Support unsigned 64-bit integers for sequence numbers

[JohnGreenan]

Is your feature request related to a problem? Please describe.
Per https://www.fixtrading.org/groups/continuousmkts/
Sequence number resets are a bore.

Describe the solution you'd like
The implementation proposed is to use an unsigned 64 bit integer for a sequence number.

Using 1 billion sequence numbers per second, that will last for 584 years until they run out.

So we can leave the problem to our great, great, great (more) grandchildren to solve!

Describe alternatives you've considered
Continuous Markets WG- 24x7 FIX Best Practise Working Draft_v0.015.docx

[JohnGreenan]

See also
da4089/simplefix#50
quickfix-j/quickfixj#621
quickfix/quickfix#419
ferrumfix/ferrumfix#108
connamara/quickfixn#760
paritytrading/philadelphia#365
jcass77/WTFIX#8
#480

[JohnGreenan]

Now adopted https://www.fixtrading.org/packages/fix-recommended-practices-24x7-sessions/