Add eachdist and move tox to root folder (#29)

Move tox and other configuration files to root folder. Add eachdist to make it
easier to handle operations with different packages.

The eachdist is taken from opentelemetry but slighty modified to avoid ignoring
a given path.

scripts/coverage.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+
+set -e
+
+function cov {
+    pytest \
+        --ignore-glob=*/setup.py \
+        --cov ${1} \
+        --cov-append \
+        --cov-branch \
+        --cov-report='' \
+        ${1}
+}
+
+
+coverage erase
+
+coverage report
+coverage xml