Merge pull request #106 from Hsn723/master

upgrade x/image dependency to support v4 and v5 bmp info headers

travis-ci: remove go versions 1.7.x .. 1.9.x

tidy up docs and comments

io: add decode option: AutoOrientation

helpers: fix race condition and simplify New

add png compression level encode option

add gif encode options

version 1.3.0