Added MPI support to the miniapp
- added ring model and all-to-all model
- started refactoring general model setup steps into a model class in
  miniapp
- optional -DWITH_MPI to turn on MPI support

merge to my fork

Remove redundant #ifdef'ed code

Address clang compiler warnings

* Add file cmake/CompilerOptions.cmake for setting up compiler
  specific options
* Disable 'missing-braces' warning on Clang
* Avoid defect in g++ 4.9.2 standard library that omits move
  constructor for `stdd::ifstream`
* Remove signed/unsigned warning in test_optional.cpp

Clang (by default) objects to the omission of parentheses in
expressios such as a && b || c, and also to brace elision
in aggregate initialisation. The latter complicates initialisation
of e.g. std::array. GCC has not turned this warning on for
that reason, and there is an open issue for this for clang:
https://llvm.org/bugs/show_bug.cgi?id=21629

* Add parentheses to resolve logical parentheses warning
* Suppress missing-braces diagnostic in test_optional.cpp

Use optional type for event_queue

* Use `#pragma once` instead of install guards
* Use `using` instead of `typedef`

* Move optionalm headers into src/util
* Change namespace for optional classes to nest::mc::util
* Include unit tests for optional and uninitialized classes
* Simplify (dedoxygenate) comments in uninitialized.hpp

Update README.md build instructions

Replace use of `std::pair<bool,T>` with `optional<T>` in
event queue code, where `optional` is taken from the
implementation defined in `external/optionalm`.

Basic synapse support

Better support tests in out-of-tree build.

Add path to data directory by preprocessor definition so that
unit tests can be run from any directory.

Synapses

This is a big and unweildy update (the last one, we promise).
- added synapses
    - update to a version of modparser that generates net_receive and
      point process currents
    - added event_queue type for queueing events in a cell
    - added advance_to() method to FVM cell that supports event delivery
    - added synapse storage and modification to cell and fvm_cell types
    - added unit tests and NEURON validation test
- include support for const_views
    - moved to more recent bcumming/vector library with support for
      const_views
    - added const-safe const_view interace to fvm_cell and matrix types

Merge Issue 18: Cleanup of includes

(yes, I'm one of 'those' programmers)

Use "" for local includes
Use <> for includes from include directories

Add all directories with files to include to CMakeLists.txt
Make all linux folder based includes global (remove the folder structure)

Use externalproject_add to manage mod->hpp depenedencies.