Update project to build with submodules

When this project is built by including it in another workspace, instead of building by command line with `carthage`, using the FRAMWORK_SEARCH_PATH of `$(PROJECT_DIR)/Carthage/Build/iOS` can produce an error, since `$(PROJECT_DIR)/Carthage/Build/iOS` might not exist.

To fix this we should use a submodule for our dependencies and include them in the RxKeyboard.xcworkspace. This will allow us to still compile the RxKeyboard library.

Author: brentleyjones

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "Carthage/Checkouts/RxSwift"]
+	path = Carthage/Checkouts/RxSwift
+	url = https://github.com/ReactiveX/RxSwift.git

RxKeyboard.xcodeproj/project.pbxproj

@@ -284,10 +284,6 @@
 				DYLIB_COMPATIBILITY_VERSION = 1;
 				DYLIB_CURRENT_VERSION = 1;
 				DYLIB_INSTALL_NAME_BASE = "@rpath";
-				FRAMEWORK_SEARCH_PATHS = (
-					"$(inherited)",
-					"$(PROJECT_DIR)/Carthage/Build/iOS",
-				);
 				INFOPLIST_FILE = "$(SRCROOT)/Supporting Files/Info.plist";
 				INSTALL_PATH = "$(LOCAL_LIBRARY_DIR)/Frameworks";
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks @loader_path/Frameworks";
@@ -309,10 +305,6 @@
 				DYLIB_COMPATIBILITY_VERSION = 1;
 				DYLIB_CURRENT_VERSION = 1;
 				DYLIB_INSTALL_NAME_BASE = "@rpath";
-				FRAMEWORK_SEARCH_PATHS = (
-					"$(inherited)",
-					"$(PROJECT_DIR)/Carthage/Build/iOS",
-				);
 				INFOPLIST_FILE = "$(SRCROOT)/Supporting Files/Info.plist";
 				INSTALL_PATH = "$(LOCAL_LIBRARY_DIR)/Frameworks";
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks @loader_path/Frameworks";