Add "goop install package" support

[dafang]

Features from this pull request

By leverage the npm command, I added the package installation support to goop install, then you can use:

• goop install to continue installing all packages from the local Goopfile file
• goop install github.com/revel/revel to install one package you specified from the command line
• goop install github.com/revel/revel #tag to install the package with the specified tag name

And also, there is one new arg supported to the install command, which is --save-dev which is the same as npm,

• goop install github.com/revel/revel --save-dev, the goop command will install the package github.com/revel/revel and it will also append the package github.com/revel/revel to the Goopfile file for convenient, or
• goop install --save-dev github.com/revel/revel which is the same as goop install github.com/revel/revel --save-dev

  Changes are made

Added the install arg support to the main.go file;

Added one new method InstallPkg to goop/goop.go file, logic:

• Create one tmp file ".Goopfile" and copy all the packages from "Goopfile" if it exists to ".Goopfile"
• Append the new package to the end of this file
• Call g.parseAndInstall(gftmp, true) to reuse the original logic to install the new packages in the file ".Goopfile"
• If --save-dev is true, then mv the tmp file ".Goopfile" to "Goopfile"

[haoxins]

:+1:

[haoxins]

@dafang is --save better?

[dafang]

same thing, --save-dev is just to make it consistent with experience with npm.

[dim]

+1