Use BinaryProvider for libz dependency

Switch to using BinaryProvider (#47)

* Switch to using BinaryProvider

* Test on Appveyor

Fixes: #46

drop 0.6, support 0.7!

remove compat, fix read! call (#44)

* Remove Compat

* correct Base method name

Closes #43

Better 0.7 support, drop 0.5

v0.6.0

.travis.yml: drop Julia 0.5 and add Julia 0.7