build/js: Fork JavaScript compilation processes

Timed comparions:

Before:
    39.169
    37.001
    36.344
    39.740
    39.276

After:
    32.287
    29.689
    30.088
    31.775
    32.275
build/Documentation: Fork marginalia process

Before:
    32.287
    29.689
    30.088
    31.775
    32.275

After:
    8.887
    8.849
    9.680
    9.937
    10.007
resources/js: Use minified analytics tracking code

Since the tracking snippet isn't going to be modified, we can treat it
as an external source and save ourselves having to minify it every time
we build.
build/css: Fork minify process
build/git: Fork install process
build: Fork cat processes
build/css: Parallelize Less CSS compilation
build/tools: Parallelize tools installation
log: Add notes from build system parallelization