Reorganize into source, assets and libraries

The C sources move to source/, the served files to assets/, the bundled
Git submodule to libraries/git and the filter scripts to extensions/.
Everything the build generates now lands in build/, so a clean is a
single remove and the tree stays clean.

1 file changed, 0 insertions, 0 deletions

diff --git a/libraries/git b/libraries/git
new file mode 160000
+Subproject 94f057755b7941b321fd11fec1b2e3ca5313a4e0