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/subprocess/subprocess.wren

@@ -0,0 +1,16 @@
+// retoor <retoor@molodetz.nl>
+
+import "subprocess" for Subprocess, ProcessResult
+
+var result = Subprocess.run("echo hello")
+System.print(result is ProcessResult) // expect: true
+System.print(result.success) // expect: true
+System.print(result.exitCode) // expect: 0
+System.print(result.stdout.trim()) // expect: hello
+
+var result2 = Subprocess.run(["/bin/echo", "world"])
+System.print(result2.stdout.trim()) // expect: world
+
+var result3 = Subprocess.run("exit 42")
+System.print(result3.success) // expect: false
+System.print(result3.exitCode) // expect: 42