Several array functions missing

[CASandmann]

I don't know exactly how many other cljs functions that aren't on the cheatsheet, but some important array functions are missing, namely amap areduce alength etc. Supposedly this pdf has a more comprehensive list of functions than the cheatsheet does, but it doesn't really document them.

[shaunlebron]

our api docs have these, but we do need to add them to the cheatsheet.

• amap
• areduce
• alength

[shaunlebron]

I think the cheatsheet's function is to provide the most commonly used functions. Will reopen if this changes.