Fix for clang 7.3 in compiling metis

This MR fixes an issue in compiling METIS on Clang 7.3, which ships with the latest OS X Xcode.

See merge request !603

Fix some LaTeX errors in doxygen.

This MR fixes some compile errors in the doxygen documentation which were not picked up on the release of 4.3.

See merge request !586

Fix eps image path for some versions of epstopdf.

This MR updates an EPS image in the developer guide to use the full path to avoid a bug in some versions of epstopdf.

See merge request !593

Fix namespace pollution

This MR removes occurrences `using namespace` in header files. This causes problems when using the library with external tools as it conflicts with other libraries (e.g. VTK).

See merge request !601

fix/meshing_TPURL

Small fix to third party urls as pointed out by spencer for the meshing side of things.
Turns out using the ae-nektar public html doesnt agree with some machines.

See merge request !606

Fix bug in DriverModifiedArnoldi

This fixes a bug in ModifiedArnoldi, which may cause the solver to exit with
```
Fatal   : Level 0 assertion violation
Unrecognised value.
```
as recently reported in nektar-users.

The problem happens because the iteration could be marked as converged when the number of vectors available is lower than `nvec`.

See merge request !608

Fix bug in Homogeneous1DTrans

This fixes a small bug in `ExpListHomogeneous1D::Homogeneous1DTrans`.

I think the particular case where this was wrong is not used anywhere, so it is very likely that nothing will change.

See merge request !599

Updated to extract directory of libccmio.a

Updated the ThirdPartyCCM.cmake file to add in Link directory and use the get_Filename_component to obtain the directory path if the library is found. This therefore allows the libccmio.a to be correctly linked from a third party location where as previous it was only compiling if the .a files were copied to the dist/lib directory. 

See merge request !600

Add option to turn off https support to solve CMake SSL woes

This MR adds a `THIRDPARTY_USE_SSL` option to enable/disable HTTPS support and fix #22, since some versions of CMake (including compute nodes and cx2 at least) are not compiled with SSL support, causing obtuse failures. The default is set to off to allow the greater range of systems to work out of the box.

See merge request !602