Added support for 32-bit AND 64-bit node download

Uses 64-bit version on 64-bit versions of Windows.
Removed arch-based directory

Wasn't really necessary.
Merge pull request #20 from coreybutler/master

Support 64-bit Node Install
add NVMW_NODEJS_ORG_MIRROR env to support custom nodejs dist mirror
/npm-versions.txt no cache