DEV: Add a devcontainer to allow codespaces development

.devcontainer/Dockerfile

@@ -0,0 +1,11 @@
+# [Choice] Debian / Ubuntu version: debian-10, debian-9
+ARG VARIANT=buster
+FROM mcr.microsoft.com/vscode/devcontainers/cpp:dev-${VARIANT}
+
+# [Optional] Uncomment this section to install additional packages.
+RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
+    && apt-get -y install --no-install-recommends libsparsehash-dev doxygen python3-dev python3-pip
+
+ENV CC=gcc-9
+ENV CXX=g++-9
+ENV PYTHON=python3

.devcontainer/base.Dockerfile

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+# [Choice] Debian / Ubuntu version: debian-10, debian-9
+ARG VARIANT=buster
+FROM mcr.microsoft.com/vscode/devcontainers/base:${VARIANT}
+
+# Install needed packages. Use a separate RUN statement to add your own dependencies.
+RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
+    && apt-get -y install build-essential cmake cppcheck valgrind clang lldb llvm \
+    && apt-get autoremove -y && apt-get clean -y && rm -rf /var/lib/apt/lists/*
+
+# [Optional] Uncomment this section to install additional OS packages.
+# RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
+#     && apt-get -y install --no-install-recommends <your-package-list-here>

.devcontainer/devcontainer.json

@@ -0,0 +1,29 @@
+{
+	"name": "C++",
+	"build": {
+		"dockerfile": "Dockerfile",
+		// Update 'VARIANT' to pick an Debian / Ubuntu OS version: debian-10, debian-9, ubuntu-20.04, ubuntu-18.04
+		"args": { "VARIANT": "ubuntu-20.04" }
+	},
+	"runArgs": [ "--cap-add=SYS_PTRACE", "--security-opt", "seccomp=unconfined"],
+
+	// Set *default* container specific settings.json values on container create.
+	"settings": {
+		"terminal.integrated.shell.linux": "/bin/bash"
+	},
+
+	// Add the IDs of extensions you want installed when the container is created.
+	"extensions": [
+		"ms-vscode.cpptools"
+	],
+
+	// Use 'forwardPorts' to make a list of ports inside the container available locally.
+	// "forwardPorts": [],
+
+	// Use 'postCreateCommand' to run commands after the container is created.
+	"postCreateCommand": "git submodule update --recursive --init && pip3 install numpy pytest sphinx sphinx_rtd_theme breathe ipython",
+
+	// Uncomment to connect as a non-root user. See https://aka.ms/vscode-remote/containers/non-root.
+	// "remoteUser": "vscode"
+
+}

.gitmodules

@@ -1,3 +1,3 @@
 [submodule "submodules/googletest"]
 	path = submodules/googletest
-	url = git@github.com:google/googletest
+	url = https://github.com/google/googletest.git