The plan goes like this:
- eeschema still uses int in decidegrees
- all the other things internally use double in decidegrees (or radians
  in temporaries)
- in pcbnew UI the unit is *still* int in decidegrees

The idea is to have better precision everywhere while keeping the user with int i
angles. Hopefully, if a fractional angle doesn't come in from the outside, everything
should *look* like an integer angle (unless I forgot something and it broke)

When the time comes, simply updating the UI for allowing doubles from the user should
be enough to get arbitrary angles in pcbnew.

New conversion routines and sin/cos implementation for angles in decidegrees

- Removed spurious int casts (these are truncated anyway and will break
  doubles)

- Applied the Distance, GetLineLength, EuclideanNorm, DEG2RAD, RAD2DEG
  ArcTangente and NORMALIZE* functions where possible

- ArcTangente now returns double and handles the 0,0 case like atan2, so
  it's no longer necessary to check for it before calling

- Small functions in trigo moved as inline

More layer classification cleanup

Better description for entities on right click menu and panel
Typo fixes and some comment reformats

Implemented the LAYER_NUM typedef (LAYER was already taken as a class name...) to represent a layer number.

- Renamed ReturnMaskLayer to GetLayerMask (since it's a plain getter)

* Complete encapsulation of the ZONE_CONTAINER class.
* Fixed a bug in the EDA_TEXT::Format() default effects behavior due to
  improper conversion to internal units and missing test for default
  thickness.
* Improved grammar of some Pcbnew context menu strings.
* Moved some more cleverly hidden BOARD object methods into class_board.cpp.
* Lots of coding policy and documentation fixes.

* Complete encapsulation of the MODULE class.
* Complete encapsulation of the EDA_TEXT class.
* Encapsulate most of the ZONE_CONTAINER class.
* Add pcbcommon library as a dependency for reSWIGging the scripting
  support.  This should cover most dependency cases.

* Encapsulate most of the MODULE class.
* Start encapsulating the DIMENSION class.
* Lay some groundwork for EDA_TEXT encapsulation.
* Move cleverly hidden MODULE functions into class_module.cpp.
* Use std::swap to exchange TEXTE_PCB values for undo/redo.
* Remove unused members from MODULE class.
* The usual coding policy and documentation fixes.

Pcbnew: Partial merge from pcad2kicad (from Alexander Lunev). Fix an old bug related to pads with offset: sometimes the connection to a zone was not detected.

* Improve the stable and testing build version option logic.
* Use CMake FindPythonInterp to configure the Python interpreter.
* Use Python interpreter to determine the system Python module install
  path if not already defined on the command line.
* Add header symbol checks for asinh(), acosh(), and atanh().
* Add test source to check for isinf() which can be defined as a C++template.
* Replace conditional compile on windows systems for aXXXh() with CMake
  configuration tests.
* A few minor MSVC compile fixes.
* Fix incorrect python environment string in fixswigimports.py
* Create a separate document for KiCad CMake build options.
* Create a separate how to compile KiCad on Windows document.

Pcbnew: Add pcad2kicad pcb plugin, to import PCAD boards ( .pcb ASCII data file PCad 2000 format ) from Alexander Lunef