Fix reading and writing of hotkey: sections in xtrn.ini

Section suffix is the decimal ASCII value, not the character itself.
Fix issue #440 as reported by Nelgin
15 jobs for new_config_format in 5 minutes and 29 seconds (queued for 20 seconds)
Status Name Job ID Coverage
  Build
passed jsdoor-freebsd #38458
FreeBSD

00:03:49

passed jsdoor-linux #38459
Linux

00:02:01

passed jsdoor-windows #38461
FreeBSD

00:01:50

passed sbbs-freebsd #38453
FreeBSD

00:05:24

passed sbbs-linux #38447
Linux

00:02:53

passed sbbs-windows #38450
Windows

00:04:59

passed sexpots-freebsd #38460
FreeBSD

00:00:11

passed sexpots-linux #38448
Linux

00:00:07

passed sexpots-windows #38451
Windows

00:00:23

passed svdm-windows #38452
Windows

00:00:22

passed syncdraw-freebsd #38456
FreeBSD

00:00:26

passed syncdraw-linux #38457
Linux

00:00:52

passed syncterm-freebsd #38454
FreeBSD

00:01:02

passed syncterm-linux #38449
Linux

00:02:14

passed syncterm-windows #38455
FreeBSD

00:01:47