yeah, there's no reference for what the entity flags could be, but i'm pretty sure that they are the first short of data for each entity. I'll also write up everything I understand about the header so far.

ok! I've got entity viewing (and rudimentary editing but NOT saving so there's no point)
 

get it get it get it  >>>> https://dl.dropboxusercontent.com/u/8943931/games/2014/KeroHackToolsv1_2.air <<<<
 
> pan the level around with WASD keys!
> reset the view with R
> TAB to switch layers, E layer to edit entities 
> Press E to toggle entity layer on or off
 
info on entity data:
 
The first byte after the tile data is the number of entities (thanks instasquid!),
then a blank byte (as far as I'm aware, its always blank)
then you start blocks of entities, which look like this:
1 byte : entity flags. need to discover more information about this thing
1 byte : entity type. in the assist/unittype.txt file, you can see a reference of all the types
2 bytes : x position
2 bytes : y position
3 bytes : unknown data. a lot of the time this is 0.
1+ bytes : a string, seems to be a script that is attached to the entity somehow. 
 
I'll get to implementing super basic entity placement soon!