Necpp

Introducing a new NEC parser. This uses ANTLR and now is fairly complete. It will have two modes, one is the compatability mode,
the other is a human readable format that is MUCH more explicit.

* Fix bug in reading comments longer than 80 characters (issue 47)
* Fixed bug in nec_context::fblock when setting up symmetry_array matrix for plane symmetry.
* Many changes to the 64-bit integer support for large matrices.

* Changes to allow compilation on CLANG. Change to use std::abs() and friends.
* Minor bug fixes in example c code.
* Minor bug in fallthrough on printing complex numbers.

* Fixed bug in helix introduced in 1.7.1 - had not updated all calls to the helix function (thanks to Yoshi Takeyasu for pointing this out)

* Changed API of c_geometry::helix() to put the tag id and segment count at the start.

* Added new functions for nec_get_gain() to get the radiation pattern elements.
* added nec_medium_parameters to the C-style API. The user can now alter the permittivity and permeability of the environment via the API.
* Added accessor methods to the radiation pattern to get all the theta and phi angles
* Added 2D matrix for radiation pattern gain_. Much easier to plot radiation patterns.
* nec_geometry_complete() now takes only one parameter. The second parameter was unused.
* New c_geometry->reflect and c_geometry->generate_cylindrical_structure(int itx, int nop) helper functions to generate symmetric structures.
* New c_ground methods for finding out the ground parameters
* Split the ground enviroment computation from the output code.
* Fix make dependencies to allow parallel make
* Allow building with gcc 5.1