Version 0.7.1

[#38] Add node 10/12 windows builds (#41)

* [#38] add node 12 windows build

* [#38] upgrade yarn to 1.22.0

* [#38] try installing NVS in before_install

* [#38] move nvs into maybe-install-node.sh and disable non windows build jobs for now

* [#38] fix .travis.yml

* [#38] use nvs 1.5.4

* [#38] build only windows for now

* [#38] use TRAVIS_NODE_VERSION for nvs

* [#38] add os: win32 to package.json

* [#38] add win32 to rustup

* [#38] exec node-pre-gyp from the cwd

* [#38] fix typo

* [#38] re-enable Linux - Node 10 build

* [#38] exec node-pre-gyp from TLD

* [#38] try ./node_modules again

* Early exist windows testing

* Use fully qualified path to pre-gyp binary

* Remove windows test build script

* Try to stop Windows builds from hanging

* Re-enable all build combinations

* [#38] only install msvc rust target if on windows; clean up

* [#38] only install msvc rust target if on windows attempt 2

* [#38] only install msvc rust target if on windows (attempt 3)

* [#38] update version to 0.7.1; update README

* Remove old commented out line in build file

Co-authored-by: Ernie Turner <ernie.turner@gmail.com>