Update minimum required C++ version for Ceres to C++14

- Removes all workarounds for pre-C++14 versions
- Removes '11' qualifier from C++ threading option and associated
  defines.
- Fix missing inclusion of 'Multithreading' in reported Ceres components
  when C++ threading model is enabled.
- Update Sphinx documentation to specify C++14 as minimum requirement.

Change-Id: I706c8b367b3221e3c4d1a0aaf669a8f9c911e438

docs/source/features.rst

@@ -54,8 +54,9 @@ Why?
     of Non-linear Conjugate Gradients, BFGS and LBFGS.
 
 * **Speed** - Ceres Solver has been extensively optimized, with C++
-  templating, hand written linear algebra routines and OpenMP or C++11 threads
-  based multithreading of the Jacobian evaluation and the linear solvers.
+  templating, hand written linear algebra routines and OpenMP or
+  modern C++ threads based multithreading of the Jacobian evaluation
+  and the linear solvers.
 
 * **Solution Quality** Ceres is the `best performing`_ solver on the NIST
   problem set used by Mondragon and Borchers for benchmarking

docs/source/installation.rst

@@ -23,9 +23,8 @@ Dependencies
 
   .. NOTE ::
 
-    All versions of Ceres > 1.14 require a **fully C++11-compliant**
-    compiler.  In versions <= 1.14, C++11 was an optional requirement
-    controlled by the ``CXX11 [Default: OFF]`` build option.
+    Starting with v2.0 Ceres requires a **fully C++14-compliant**
+    compiler.  In versions <= 1.14, C++11 was an optional requirement.
 
 Ceres relies on a number of open source libraries, some of which are
 optional. For details on customizing the build process, see
@@ -378,7 +377,7 @@ Windows
   <https://github.com/tbennun/ceres-windows>`_ for Ceres Solver by Tal
   Ben-Nun.
 
-On Windows, we support building with Visual Studio 2013 Release 4 or newer. Note
+On Windows, we support building with Visual Studio 2015.2 of newer. Note
 that the Windows port is less featureful and less tested than the
 Linux or Mac OS X versions due to the lack of an officially supported
 way of building SuiteSparse and CXSparse.  There are however a number
@@ -709,7 +708,7 @@ Options controlling Ceres configuration
    gains in the ``SPARSE_SCHUR`` solver, you can disable some of the
    template specializations by turning this ``OFF``.
 
-#. ``CERES_THREADING_MODEL [Default: CXX11_THREADS > OPENMP > NO_THREADS]``:
+#. ``CERES_THREADING_MODEL [Default: CXX_THREADS > OPENMP > NO_THREADS]``:
    Multi-threading backend Ceres should be compiled with.  This will
    automatically be set to only accept the available subset of threading
    options in the CMake GUI.
@@ -904,8 +903,6 @@ The Ceres components which can be specified are:
 #. ``Multithreading``: Ceres built with *a* multithreading library.
    This is equivalent to (``CERES_THREAD != NO_THREADS``).
 
-#. ``C++11``: Ceres built with C++11.
-
 To specify one/multiple Ceres components use the ``COMPONENTS`` argument to
 `find_package()
 <http://www.cmake.org/cmake/help/v3.2/command/find_package.html>`_ like so:

docs/source/nnls_solving.rst

@@ -2226,7 +2226,7 @@ The three arrays will be:
    Number of threads actually used by the solver for Jacobian and
    residual evaluation. This number is not equal to
    :member:`Solver::Summary::num_threads_given` if none of `OpenMP`
-   or `CXX11_THREADS` is available.
+   or `CXX_THREADS` is available.
 
 .. member:: LinearSolverType Solver::Summary::linear_solver_type_given