Lock istanbul to v0.1.37 to prevent breaking coverage comparison tests.
Omit assets in non-skinnable builds when mod.assets === false

When a module's build config includes the "assets" property set to `false`,
we should skip copying any existing assets folder for that build target.

However, if that module's meta.json includes the "skinnable" property set
to true, the assets directory will still be copied, as it is required by
the skinning pattern.

Fixes #87
Merge pull request #91 from zillow/lock-istanbul

Lock istanbul to v0.1.37 to prevent breaking coverage comparison tests
Merge pull request #92 from zillow/omit-assets

Omit assets in non-skinnable builds when mod.assets === false
bumping version. adding new npm command to generate docs easily. updated docs.
move `args.unshift(util.shifter)` out of walk.js's run() loop

The path 'shifter/bin/shifter' was prepended to the spawn argument list
on each iteration of run(), which can be called many times in walk.js.
This grew the argument list. The extra args are ultimately ignored, but
this small fix prevents non-parsed arg pollution (i.e. the values nopt
returns in the parsed.remain property).