Add dependency to shelljs

shelljs (https://www.npmjs.org/package/shelljs) allows unix command to be executed on Windows.

gh-1
Apply shelljs methods to unix operation

Replace execution of unix related operations such as cp, rm, and cat with shelljs' methods to support cross platform.

gh-1
Add 'force' parameter to copy operation

Without -f content of dist will remain the same.

gh-1
Add build option for Windows

gh-1
Update with build instruction for Windows user

Closes gh-1
Merge branch 'master' of https://github.com/rashidi/swagger-ui

Conflicts:
	README.md