Translations severe update

[nerun]

Where to start from?

1) Translations: updated 'es', 'fr', 'it' and 'ru.po' to line up help message (PR #481 and Jaromil request in PR #483).

One request before merging, which should be easy to do: can you please also update the .po translations with this detail? so we keep them aligned.

Done. I used a script to print help output out of PO files and check all them:

#!/usr/bin/env zsh
clear
egrep -A 141 'Syntax:' $1 | 
egrep -v "^(#|msgid|\s*$)" | 
sed 's/msgstr \"//g' | 
sed 's/\" / /g' | 
grep -v "^\"" |
sed 's/\"$//g'

Not important, just saying.

2) Updated Brazilian Portuguese translation (pt_BR). Also updated Makefile to include this translation.

Related to issue #482. I have translated to pt_BR before Weblate was created, sorry. But thank you for that.

3) Added Brazilian Portuguese (pt_BR) translation (for Tomb 2.10). Also created tomb.pot template for version 2.10.

Hard to explain, better to read the ne created README for extras/translations folder. It's all very well explained there.

4) Created a README file in extras/translations to clear up confused issues about translations versions.

This is a huge point, ALL translations in extras/translations are based upon Tomb 2.3, not the current 2.10 or the stable 2.9. I think i have explained it very well in README. Please read it.

[nerun]

You can see the README file, in my fork right here.

[nerun]

@jaromil , can you take a look in this PR? I can split it in different commits if needed.

[jaromil]

This looks very well done. Thanks for the README!