For each package-level entity we emit one or more Decl struct, which
contains all JS code fragments and metadata required to produce the
final executable script.

For each decl type (imports, vars, functions and types) I created a
separate function that contains the logic responsible for its creation
(and some auxiliary functions). The main objective is to keep the
Compile() function very high-level and clearly reflecting various
compilation stages we go through.

I tried to add comments to make the code more accessible for future
contributors (and future self...), although there are still some aspects
I don't fully grasp.

Ideally, we would have tests for all these new functions, but that's way
more work than I'm able to take on right now.

(based on commit 146735d)

compiler: break functions related to Decls out of Compile().

The logic is already very complicated and breaking it up into more
manageable methods will improve readability.

 - Broke out nestedFunctionContext() and translateStandaloneFunction()
 - Removed the need to return function param names from
   translateFunctionBody()

(based on commit 2e9a5ce)

Move function translation code into a separate file.