Implemented MCDU AIRWAYS page

[noteas]

Description of Changes

Dear A320-family contributors,

Merry Christmas Eve. After several days' work, I have roughly implemented MCDU AIRWAYS page, solving issues #280 and #283. However, it may still need further testing, especially in a complete flight. By the way, I added a link of a detailed guide for navdata installation on FG Wiki to README.md.

Looking forward to your early reply.

Best wishes,
noteas

Screenshots (optional)

Checklist:

• My changes follow the Contributing Guidelines.
• My changes implement realistic features.
• Please have a main Developer test my changes before merging.

[merspieler]

Thank you very much.
We'll take a look at it.

I also wish you a merry xmas.

[legoboyvdlp]

Are we sure that DCT legs can in fact be inserted using the AIRWAYS page?

[merspieler]

Afaik no, you enter the airway and your exit way point til which you follow the airway, there're no DCT legs

[legoboyvdlp]

Yes, that's what I was wondering, I thought the standard practice was using NEXT WPT to insert DCT legs.

[merspieler]

yep

[legoboyvdlp]

Actually thinking, maybe it would be worth merging this ... even though it's not strictly correct, at least it can be used as a base, and then after FlightGear 2020.4, the airways API can be included?

@merspieler ?

[merspieler]

@legoboyvdlp I'm not really familiar with that part of the code, I trust your judgment on this.
From a project side of view, both sound fine to me.

[merspieler]

@legoboyvdlp this pr is still open, you did suggest merging it, what do you say?

[merspieler]

I'm getting an error, entering the following route
EDDM TURB6S TURBU Y107 ASVUT Q984 VOG M858 LIGUR LIGU2L LFKC
I've first entered SID and STAR, then went TURBU - > AIRWAYS entered Y107. upon trying to enter ASVUT I got the following error:

  953.95 [ALRT]:nasal      Nasal runtime error: flightplan.indexOfWP called on leg from different flightplan
  953.95 [ALRT]:nasal        at /games/.fgfs/Aircraft/A320-family/Nasal/MCDU/AIRWAYS.nas, line 83
  953.95 [ALRT]:nasal        called from: /games/.fgfs/Aircraft/A320-family/Nasal/MCDU/MCDU.nas, line 992
  953.95 [ALRT]:nasal        called from: , line 1

[legoboyvdlp]

As far as I'm aware the merge request is only to add DCT legs, not airways? That being said, it shouldn't result in a nasal error if you try to add an airway, it should fail with a scratchpad message (e.g. "NOT IMPLEMENTED");

The reason is because the airways API was not made functional yet in the stable versions of flightgear, also because I can't run 2020.4 on Intel hardware (it stops rendering - yes, literally) I can't make it functional.

The E-jet-family is the only one that I know of that does work at this time

[merspieler]

I've got no clue, just tested it... maybe at @noteas can take a look at it.
And what if we condition the page call to the version, like we do it with that one canvas attribute for example?