automate installation of shell scripts

[mcandre]

Provide a short, simple, copy & paste friendly command to install shell script applications.

Follow modern best practices, such as separating the curl / wget download from script execution into two separate commands, for security and auditing purposes.

Document a requirement that at least one POSIX compliant shell is available to run the (POSIX sh based) installer.

Document a requirement that curl and tar are installed.

Similar to RVM, chruby, and other common shell based installers, we could check for ~/.profile (bash family), ~/.zshrc (zsh), ~/.kshrc (ksh), ? (fish), ? (Plan 9 rc), ? (ion). When a matching file is found, then automatically append a PATH appending command to the file, and log that this has been done to the file.

Research (ideally POSIX sh) tools to aid this process. Hopefully, those tools have gone through a lot of testing, although they likely are not thinking about extreme portability and probably artificially exclude many fringe platforms.