v0.3.0

Changelog

b1962b9 ensure tmp image is cleaned up on crash (addresses part of #58)
7d86809 use env vars to determine the docker API version (closes #71)
6a6cbe1 add docs for filetree screen width
49baf84 configurable filetree split col (addresses #69)
30f3fed add image size to details pane (closes #66)
3c46874 add dir collapse docs
64d1a3b configurable directory collapse default value (closes #70)
e153cb4 Update README.md (#68)
e0af39c bump version ref