Colorize stacktrace and use : before printing line number

[fuelen]

Hello

Here, Jose mentioned that it would be great to send some improvements present in https://github.com/fuelen/ecto_dev_logger to upstream: phoenixframework/phoenix_ecto#152 (comment)

This is the first patch.

Changes:

• colorize stacktrace (returning to the original color is not needed, as this is the last part of the string)
• use : before printing line number, as this format helps editors to open the file at the specified line

[josevalim]

💚 💙 💜 💛 ❤️