Feature/opencv4 (#706)

* Travis OpenCV4 update, testing Ubuntu with new OpenCV

* Fix to Ubuntu travis

* Another attempt at OpenCV 4.0 for Ubuntu

* And another OpenCV attempt.

* Simplifying the travis script

* Ubuntu OpenCV 4 support.

* Updating to OpenCV 4, for x64 windows.

* Fixes to move to OpenCV 4 on windows.

* Travis fix for OpenCV 4 on OSX

* Renaming a lib.

* Travis opencv4 fix.

* Building OpenCV4 versions using appveyor.

* Attempt mac travis fix.

* Small travis fix.

* Travis fix attempt.

* First iteration in boost removal and upgrade to C++17

* Test with ocv 4.0

* Moving filesystem out of stdafx

* Some more boost testing with cmake.

* More CMAKE options

* More compiler flag changes

* Another attempt at compiler options.

* Another attempt.

* More filesystem stuff.

* Linking to filesystem.

* Cmake fix with target linking.

* Attempting travis with g++-8

* Attempting to setup g++8 on travis linux.

* Another travis change.

* Adding OpenBLAS to travis and removing g++-8

* Fixing typo

* More travis experiments.

* More travis debugging.

* A small directory change.

* Adding some more travis changes.

* travis typo fix.

* Some reordering of travis, for cleaner yml

* Removing `using namespace std` in order to avoid clash with byte and to make the code more consistent.

* Working towards removing std::filesystem requirement, allow boost::filesystem as well.

* Making boost an optional dependency

* Fixing std issue.

* Fixing cmake issue.

* Fixing the precompiled header issue.

* Another cmake boost fix.

* Including missing files.

* Removing unnecessary includes.

* Removing more includes.

* Changes to appveyor build, proper removal of VS2015

* If boost is present, do not need to link to filesystem.

* Removing un-needed link library.

* oops

* Mac attempt at opencv4 travis.

* Upgrading OCV to 4.1 on VS2018

* Downloading OpenCV binaries through a script

* Triger an appveyor build.

* Upgrading VS version.

* Attempting VS2017 build

* Adding win-32 libraries for OpenCV 4.1

* Adding OpenCV 32 bit libraries.

lib/3rdParty/OpenCV/include/opencv2/imgcodecs/legacy/constants_c.h

@@ -0,0 +1,54 @@
+// This file is part of OpenCV project.
+// It is subject to the license terms in the LICENSE file found in the top-level directory
+// of this distribution and at http://opencv.org/license.html.
+
+#ifndef OPENCV_IMGCODECS_LEGACY_CONSTANTS_H
+#define OPENCV_IMGCODECS_LEGACY_CONSTANTS_H
+
+/* duplicate of "ImreadModes" enumeration for better compatibility with OpenCV 3.x */
+enum
+{
+/* 8bit, color or not */
+    CV_LOAD_IMAGE_UNCHANGED  =-1,
+/* 8bit, gray */
+    CV_LOAD_IMAGE_GRAYSCALE  =0,
+/* ?, color */
+    CV_LOAD_IMAGE_COLOR      =1,
+/* any depth, ? */
+    CV_LOAD_IMAGE_ANYDEPTH   =2,
+/* ?, any color */
+    CV_LOAD_IMAGE_ANYCOLOR   =4,
+/* ?, no rotate */
+    CV_LOAD_IMAGE_IGNORE_ORIENTATION  =128
+};
+
+/* duplicate of "ImwriteFlags" enumeration for better compatibility with OpenCV 3.x */
+enum
+{
+    CV_IMWRITE_JPEG_QUALITY =1,
+    CV_IMWRITE_JPEG_PROGRESSIVE =2,
+    CV_IMWRITE_JPEG_OPTIMIZE =3,
+    CV_IMWRITE_JPEG_RST_INTERVAL =4,
+    CV_IMWRITE_JPEG_LUMA_QUALITY =5,
+    CV_IMWRITE_JPEG_CHROMA_QUALITY =6,
+    CV_IMWRITE_PNG_COMPRESSION =16,
+    CV_IMWRITE_PNG_STRATEGY =17,
+    CV_IMWRITE_PNG_BILEVEL =18,
+    CV_IMWRITE_PNG_STRATEGY_DEFAULT =0,
+    CV_IMWRITE_PNG_STRATEGY_FILTERED =1,
+    CV_IMWRITE_PNG_STRATEGY_HUFFMAN_ONLY =2,
+    CV_IMWRITE_PNG_STRATEGY_RLE =3,
+    CV_IMWRITE_PNG_STRATEGY_FIXED =4,
+    CV_IMWRITE_PXM_BINARY =32,
+    CV_IMWRITE_EXR_TYPE = 48,
+    CV_IMWRITE_WEBP_QUALITY =64,
+    CV_IMWRITE_PAM_TUPLETYPE = 128,
+    CV_IMWRITE_PAM_FORMAT_NULL = 0,
+    CV_IMWRITE_PAM_FORMAT_BLACKANDWHITE = 1,
+    CV_IMWRITE_PAM_FORMAT_GRAYSCALE = 2,
+    CV_IMWRITE_PAM_FORMAT_GRAYSCALE_ALPHA = 3,
+    CV_IMWRITE_PAM_FORMAT_RGB = 4,
+    CV_IMWRITE_PAM_FORMAT_RGB_ALPHA = 5,
+};
+
+#endif // OPENCV_IMGCODECS_LEGACY_CONSTANTS_H