Initial Julia 0.6 support release

Merge pull request #97 from JuliaWeb/yyc/0.6

Fix depwarn on 0.6

v0.4.3: Merge pull request #96 from JuliaWeb/tk/dontexit

Use a goto instead of exit() to fix #93

v0.4.2: Add +x to deps/cmake_check.sh (#91)

This appears to be necessary even when installing older releases of
this package.

v0.4.1: Merge pull request #90 from JuliaWeb/jq/build

Add a fallback build.jl step in case correct system libraries aren't detected

v0.4.0: Merge pull request #83 from JuliaWeb/jq/79

Check if ctx.config is defined before calling get_version; technicall…

v0.3.1

Update MbedTLS to conform to the TransportLayerSecurity.jl API