Add integration to conan.io package manager

Unfortunately not all cmake tests pass during the packaging so they had
to be disabled for the time being. This is due to conan changing the
project directories during packaging.

Feel free to distribute this great library with conan to for example
bintray.

conanfile.py

@@ -0,0 +1,47 @@
+from conans import ConanFile, CMake, tools
+from conans.tools import load
+import re
+
+def get_version():
+    try:
+        content = load("CMakeLists.txt")
+        version = re.search(b"project\(nlohmann_json VERSION (.*) LANGUAGES CXX\)", content).group(1)
+        return version.strip()
+    except Exception as e:
+        return None
+
+class JsonConan(ConanFile):
+    name = "json"
+    version = get_version()
+    license = "MIT"
+    url = "https://github.com/nlohmann/json/"
+    description = "JSON for Modern C++"
+    author = "Niels Lohmann (mail@nlohmann.me)"
+    generators = "cmake"
+    exports_sources = "include/*"
+    no_copy_source = True
+    scm = {
+        "type": "git",
+        "url": "auto",
+        "revision": "auto"
+    }
+
+    def build(self):
+        cmake = CMake(self)
+        cmake.configure()
+        cmake.build()
+
+    def source(self):
+        self.run("git clone https://github.com/nlohmann/json/")
+        self.run("cd json")
+        tools.replace_in_file("CMakeLists.txt",
+                              "project(nlohmann_json VERSION {version} LANGUAGES CXX)".format(version=self.version),
+                              '''PROJECT(nlohmann_json VERSION {version} LANGUAGES CXX)
+include(${{CMAKE_BINARY_DIR}}/conanbuildinfo.cmake)
+conan_basic_setup()'''.format(version=self.version))
+
+    def package(self):
+        self.copy("include/*.hpp")
+
+    def package_id(self):
+        self.info.header_only()