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/env/environment.wren

@@ -0,0 +1,19 @@
+import "env" for Environment
+
+Environment.set("WREN_TEST_VAR", "hello")
+System.print(Environment.get("WREN_TEST_VAR")) // expect: hello
+
+Environment.set("WREN_TEST_VAR", "world")
+System.print(Environment.get("WREN_TEST_VAR")) // expect: world
+
+Environment.delete("WREN_TEST_VAR")
+System.print(Environment.get("WREN_TEST_VAR") == null) // expect: true
+
+System.print(Environment.get("THIS_VAR_DOES_NOT_EXIST") == null) // expect: true
+
+var home = Environment.get("HOME")
+System.print(home != null) // expect: true
+
+var all = Environment.all
+System.print(all is Map) // expect: true
+System.print(all.count > 0) // expect: true