Eclectica

Specifically important for python and ruby proxy

* For nodejs – reinstall global node_modules during version switch only if newly introduced flag `--with-modules` is provided

* Improve installation of python and ruby

* Output more data to stdout during the compilation process

* Introduce locks and mutex

* More detailed error log output

* Output stderr only to stderr channel

* Improve golang installation and view

* Improve semver sorting in "ls" output

* Refactoring of the `New` signatures

* Make tests execution stable

...and more small stuff

* Improve yarn installation

* Simplify & and speed up modules installation during switch between versions of node

* Add hidden command for PATH output and install it to shell config

* Fix various small bugs

* Refactoring of the main functionality

* More tests

* Speed up compilation for languages that needed it

* Change the way of go installation (go1.9 could be installed now) and some structure augmentations

* Speed up Ruby installation, decide on the fly to either download or compile it

* Make errors output verbose

* Improve nodejs installation

* Outline the travis matrix and supported systems