Add basic snapcraft yaml for building a snap

src/snap/snapcraft.yaml

+name: visualboyadvance-m
+version: 2.1.0
+summary: Nintendo Game Boy Advance Emulator
+description: |
+  An open-source Nintendo Game Boy, Super Game Boy, Game Boy Advance Emulators.
+
+confinement: devmode
+
+parts:
+  vbam:
+    source: https://github.com/visualboyadvance-m/visualboyadvance-m/archive/v2.1.0.tar.gz
+    plugin: cmake
+    build-packages:
+      - g++
+      - gcc
+      - make
+      - cmake
+      - libwxgtk3.0-dev
+      - libsdl2.0-dev
+      - libsfml-dev
+      - libgtk-3-dev
+    configflags:
+      - -DCMAKE_INSTALL_PREFIX=/
+
+apps:
+  visualboyadvance-m:
+    command: visualboyadvance-m