that actually looks like a fairly easy one to learn with, I recommend giving it a try in the editor.
a short how to to get you started:
1) tool your looking for is the data file editor in tools > launch editor
2) from there you're going to want to create a base class ("class" tab), hit new(blank)
3) now enter appropriate details, for custom stuff I usually end the ident or begin it with a C, in this case CMi
4) now its a fairly simple fill in the fields job, making sure to set class skills and save/bab progression in the selectors
5) Class features. fortunately, your major ones, the bonus feats and animal companion are direct rips from other classes, so adding those is fairly trivial. select animal companion in "choose companion type" and make sure you put 1 in "companion at level"
6) fighter bonus feats are easy, simply count up as you go, putting the numbers in row(level-1) [example: 0=1, 1=2, 4=3, 7=4, etc]
7) set bonus feat allowed as "bonus for: fighter"
from here is where things get interesting. trhe easiest way to learn how to code class specials is to look for other class features that do the same thing or similar, and alter the effect as needed. (simply hit new(copy) in class specials and grab the one you want, remember to delete the record afterwards so as not to create a duplicate!)
for example, con to AC is done by the dwarven defender, so you could pull the appropriate special and then look at how the eval script is written to handle that.
for situational modifiers, (the touching the ground stuff) I would enter as a non-functional special with full text and leave it to the player to figure out if they meet the conditions and apply it as appropriate. HL isn't very good at very situational modifiers, about as far as it goes is permanent effects relating to other character options, like ninja or swashbuckler only using class abilities while unarmored.
aside from eval scripts for certain effects, most stuff is actually pretty straightforward. I suck at programming and I can still manage most things.
the help ?s are always your friend, and if you've searched and searched and there isn't an existing example of some oddball ability, that's what this forum is for
