feat: add cJSON and SQLite amalgamation source files under deps/

Add the cJSON library (cJSON.c, cJSON.h) and SQLite amalgamation
(sqlite3.c, sqlite3.h, sqlite3ext.h, shell.c) as vendored dependencies
in the deps/ directory for use by the project build system.

test/signal/signal.wren

@@ -0,0 +1,10 @@
+// retoor <retoor@molodetz.nl>
+
+import "signal" for Signal
+
+System.print(Signal.SIGINT) // expect: 2
+System.print(Signal.SIGTERM) // expect: 15
+System.print(Signal.SIGHUP) // expect: 1
+System.print(Signal.SIGQUIT) // expect: 3
+System.print(Signal.SIGUSR1) // expect: 10
+System.print(Signal.SIGUSR2) // expect: 12