Add Type and methods to build command pipelines and command lists

[vladimirvivien]

Echo users should be able to pipe one command's io output stream into a subsequent command

Create a Pipe Builder

A pipe builder builds a sequence of commands where the result of the one command is used as input for next command.

e.Pipe("echo $HOME").Into("grep vivien").Run()

• Pipe creates type Pipe
• Pipe.Into(string command) adds command to the pipe
• Pipe.Run() terminates and execute the commands in the pipeline

All piped commands must terminate with a Proc result of zero to be successful. If a pipe fails, the pipe terminator method (see below) will stop and return immediately. The pipe can be configured with an all-or-none configuration where all commands must succeed. Another configuration should allow a command to fail and continue.

Pipe Terminators

• Pipe.Run() Executes and terminates the pipe result and returns the result as a string
• Pipe.RunProc Executes and terminates the pipe and returns a Proc for further processing (see echo.RunProc)
• Pipe.StartProc Executes pipes in a separate goroutine and returns a Proc to inspect the running process

[vladimirvivien]

This was implemented with #43