build heroku style log coloring into the papertrail-cli

[diwu1989]

the colortail command and sample file doesn't color the log the same way heroku papertrail does it.

you really should just build the color functionality into papertrail-cli

[troy]

Yeah, I agree. I find myself using the heroku logs more than I should, purely because of the color. I think what it does is the minimum.

Can you think of ways we can improve upon what heroku logs (in a buildpack-agnostic way)? For example, would you prefer if the colorization was based on dyno ID as well as dyno type? Something else?

[troy]

More implementation notes:

• goal is to consistently colorize timestamp, hostname, and program/filename, using a color chosen from among a palette of 5 which are visible on both black and white backgrounds. The colors are here, excluding black, white, and blue (hard to distinguish from cyan)
• color should be chosen based on the hostname+program pair, then used for all logs from that hostname+program throughout at least that 1 invocation. >1 hostname+program pairs may have the same color, since there will often be far more than 5 hostname+program pairs. For now and probably for release, feel free to use something like (hostname.length + program.length) % 5 as the index to a colors array
• colorize portion of output from start of line up to and including the : prior to the start of the message. Example portion of output which would be colorized: Sep 25 16:13:15 www23 app/web.2:
• probably using something like the ansi gem.
• here's Heroku's implementation, which is the inspiration for this behavior but operates on only the program/filename.

[troy]

Also:

• honor this to decide whether to enable/disable it
• papertrail-cli is licensed under the MIT License, as is heroku-cli, so if any or all of that log displayer class is reusable, feel free to do so