Release 0.3

Enhancements
===========

- Unified Inch Screw Threads

Fixes
===========

- PCO-1881 internal (minor diameter was too small)
- Dpitch problem with G-ext threads

Improvements
===========

- developer docs
- build system
- unit tests
- user does not need to rotate internal threads by 180 deg anymore
to fit external thread

!! Incompatibel changes !!
====================

We take the liberty to do this while the major version is still 0:

- internal thread is rotated by 180 deg (see improvements). nut() and bolt() are not affected by this

docs/MetricThread.md

@@ -0,0 +1,15 @@
+# Metric Thread
+
+![Metric thread specs](http://mdmetric.com/tech/din13pix.jpg)
+
+metric_thread.csv provides the numbers given in the norm (no thinking done there, just copying). metric_thread.awk - as usual - calculates the threadlib specs. 
+
+- Designator: use the simplified variant
+- Pitch diameters: Choose the center of the tolerance range
+- Support diameters: Center of tol. range
+- Valley diameter: Border of tol. range so that overlap with support is assured
+- Crest diameters: Center of tol. range
+
+## Specialties
+
+For some internal threads, we get a valley diameter that is on the corner or even outside the fundamental triangle. This would lead to one turn of the thread overlapping with the next turn which we need to avoid. Therefore, we have a built-in check to limit the valley diameter to a safe range.