Metric bolts library

# Summary

OpenSCAD library for Metric bolts and nuts with exact Metric thread profiles.
It can generate threads alone or in a bolt/screw or nut.

The library allows to generate STL for threads from M1.6 to M64 and from MF1.6 to MF64.

The STL for M5 and M6 bolts and nuts are provided in thing files to show the results.

# List of predefined threads
- This list can be extended with the API
- Available in standard coarse and fine threads
M1.6, M2, M2.5, M3, M4, M5, M6, M8,
M10, M12, M14, M16, M18,
M20, M22, M24, M27,
M30, M33, M36, M39,
M42, M45, M48, M52, M56,
M60, M64

# Howto

Sample OpenSCAD file to render a M6 bolt in **Metric Coarse** standard:
```
use
use

$fn=100;
mxBoltHexagonalThreaded( M6() );

```

Sample OpenSCAD file to render a M6 bolt in **Metric Fine** standard:
```
use
use

$fn=100;
mxfBoltHexagonalThreaded( MF6() );

```

# Documentation

Detailed documentation available on [GitHub Wiki](ht