Add conan support. Bring Expat, Zlib and libcurl using conan

conanfile.py

@@ -0,0 +1,11 @@
+from conans import ConanFile
+from conans.tools import os_info
+
+class Exiv2Conan(ConanFile):
+    settings = 'os', 'compiler', 'build_type', 'arch'
+    generators = 'cmake'
+
+    def requirements(self):
+        self.requires('Expat/2.2.1@pix4d/stable') # From pix4d
+        self.requires('zlib/1.2.11@conan/stable') # From conan-center
+        self.requires('libcurl/7.47.1@lasote/stable') # From conan-transit (It also brings OpenSSL)

config/findDependencies.cmake

@@ -1,6 +1,12 @@
 # set include path for FindXXX.cmake files
 set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_SOURCE_DIR}/config/")
 
+# Check if the conan file exist to find the dependencies
+if (EXISTS ${CMAKE_BINARY_DIR}/conanbuildinfo.cmake)
+    include(${CMAKE_BINARY_DIR}/conanbuildinfo.cmake)
+    conan_set_find_paths()
+endif()
+
 find_package(Threads REQUIRED)
 
 if( EXIV2_ENABLE_PNG )