add .Doxyfile: the default Doxygen config file from `doxygen -g`
add "make {docs,doxygen}" targets to build doxygen-generated docs
.gitignore doxygen-generated documentation
.Doxyfile: modify to generate C++ docs, excluding tests
.Doxyfile: don't warn if undocumented (maybe someday...)
layer.hpp: Doxygen-style documentation
loss_layers.hpp: Doxygen-style documentation
neuron_layers.hpp: Doxygen-style documentation
common_layers.hpp: Doxygen \brief & TODO stubs.
data_layers: Doxygen \brief & TODO stubs.
vision_layers.hpp: Doxygen \brief & TODO stubs.
filler.hpp: add brief filler descriptions
blob.hpp: a little Doxygen-style documentation
syncedmem.hpp: \brief and todo
solver.hpp: add \briefs
net.hpp: Doxygen-format docs