Added eigen3-nnls as git submodule

This contains a NNLS solver, which we use to solve for the blendshape coefficients.

.gitmodules

@@ -7,3 +7,6 @@
 [submodule "3rdparty/glm"]
 	path = 3rdparty/glm
 	url = https://github.com/g-truc/glm.git
+[submodule "3rdparty/eigen3-nnls"]
+	path = 3rdparty/eigen3-nnls
+	url = https://github.com/hmatuschek/eigen3-nnls.git

eigen3-nnls @ d20add35

+Subproject commit d20add35bcfc9932671cab9ad786b24fd320a592

CMakeLists.txt

@@ -97,6 +97,7 @@ message(STATUS "Eigen3 version: ${EIGEN3_VERSION}")
 set(CEREAL_INCLUDE_DIR "${CMAKE_SOURCE_DIR}/3rdparty/cereal-1.1.1/include")
 set(glm_INCLUDE_DIR "${CMAKE_SOURCE_DIR}/3rdparty/glm")
 set(nanoflann_INCLUDE_DIR "${CMAKE_SOURCE_DIR}/3rdparty/nanoflann/include")
+set(eigen3_nnls_INCLUDE_DIR "${CMAKE_SOURCE_DIR}/3rdparty/eigen3-nnls/src")
 
 # Header files:
 set(HEADERS
@@ -140,6 +141,7 @@ include_directories(${OpenCV_INCLUDE_DIRS})
 include_directories(${EIGEN3_INCLUDE_DIR})
 include_directories(${glm_INCLUDE_DIR})
 include_directories(${nanoflann_INCLUDE_DIR})
+include_directories(${eigen3_nnls_INCLUDE_DIR})
 
 # Custom target for the library, to make the headers show up in IDEs:
 add_custom_target(eos SOURCES ${HEADERS})