Plugin should not modify the build environment

[britter]

This plugin has a sophisticated system for making the shellcheck binary available by calling various package managers. This modifies the build environment by adding a binary into the PATH. This is a surprising side-effect. I want my build to be contained in the project directory and not tamper with my system.

Instead of using package managers to install shellcheck, this plugin should instead add a custom Ivy repository to the build and then define a dependency on the shellcheck GitHub release. It has to detect the current OS and system architecture to select the correct variant. An artifact transform can be used to untar the binary. The command line for running shellcheck can then be constructed using the unpack location.