Resend macros

[VictorDenisov]

This is another approach to solving this problem: #332.
Compared to #360 this PR minimally touches existing code.
It's easier to prove that this code doesn't break any existing behavior.
We can make new behavior configurable if you are not certain whether it can suit everyone.

[zcsahok]

Re-sent serial has one leading zero less:

[zcsahok]

Re-sent serial looks OK now.

[VictorDenisov]

I think I addressed all comments.

[zcsahok]

Thanks, will make a final test tomorrow.

Two minor points:
Please check the man page if it needs an update.
Apply source formatting to the changed files: we use astyle with the setting in tools/astylerc

sendbuf.c has a merge conflict now due to #358, but I can merge it manually, no problem.

[zcsahok]

Just for the record, there are two minor issues related to the re-send functionality in general.
For normal contest operation these are not really relevant, but nevertheless shall be fixed to have a consistent behavior.

• an eventual correction of RST of the previous QSO is not honored: the value
  of last_rst global is sent instead of the actual one from the last QSO.

• confirm call (=) does not respect correction of call. Same story as above:
  global lastcall is used instead of a QSO field. In addition, its value
  is initially empty so after start-up last call can't be confirmed.

Both globals have to be dropped and this will require a separate PR.

[VictorDenisov]

I didn't quite understand the comment about confirm call. But I fixed rst field.

[zcsahok]

Thanks for the RST fix! Please also remove the global variable last_rst as it is now written only.

S&P works now OK.

For confirming call I meant the message sent on pressing =. It is useful for CQ mode only and shall send the previous call. But let's check this separately.

[zcsahok]

Thanks!

Merged in master to resolve the merge conflict.