Update for Italian translations

[phyver]

@Mte90
I've modified a couple of things and some Italian translations would need some updates.

• new messages in missions 19 and 20 (file it.po in $GSH_MISSIONS/intermediate/05_background/i18n/ and $GSH_MISSIONS/intermediate/06_control-C/i18n/)
• new warning in the global $GSH_ROOT/i18n/it.po, as well as a couple of older missing translations (I counted 5 missing translations in total)
• new option for gameshell.sh and splitting the help into a "full" help and a "short" help message (files $GSH_ROOT/i18n/start-help/it.txt and $GSH_ROOT/i18n/start-full-help/it.txt: options -h, -H and -I, and the additional "usage" header, cf the English version)

Can you have a look when you get some spare time?

[phyver]

Sorry for the delay.
I merged your changes a few minutes ago (#bad0ecf9)

I also started writing a manpage for gsh which contains the same information as the gsh HELP command, formatted in a Unix manpage style. To avoid duplication, both the "full help" message and the manpage are generated (using asciidoc) from the same files containing the commands descriptions. Only some header / footer differ.

Right now, I did that in English and French. There is no italian manpage, and the italian file used for "gsh HELP" is the original one.

This is pretty much work in progress. You can translate the header file for the "gsh HELP" command, but the manpage itself might still change.

If you want to have a look, I pushed those commits to the "dev" branch, with a long commit message explaining where the files are located, and what to do with them.
(Beware, I regularly force push there.)

[Mte90]

I prefer to wait when is finished as I can be busy :-)