[xml] Initial implementation of core:encoding/xml.

A from-scratch XML implementation, loosely modeled on the [spec](https://www.w3.org/TR/2006/REC-xml11-20060816).

Features:
		- Supports enough of the XML 1.0/1.1 spec to handle the 99.9% of XML documents in common current usage.
		- Simple to understand and use. Small.

Caveats:
		- We do NOT support HTML in this package, as that may or may not be valid XML.
		  If it works, great. If it doesn't, that's not considered a bug.

		- We do NOT support UTF-16. If you have a UTF-16 XML file, please convert it to UTF-8 first. Also, our condolences.
		- <[!ELEMENT and <[!ATTLIST are not supported, and will be either ignored or return an error depending on the parser options.

TODO:
- Optional CDATA unboxing.
- Optional `&gt;`, `&#32;`, `&#x20;` and other escape substitution in tag bodies.
- Test suite

MAYBE:
- XML writer?
- Serialize/deserialize Odin types?

tests/core/encoding/json/test_core_json.odin

@@ -0,0 +1,90 @@
+package test_core_json
+
+import "core:encoding/json"
+import "core:testing"
+import "core:fmt"
+
+TEST_count := 0
+TEST_fail  := 0
+
+when ODIN_TEST {
+	expect  :: testing.expect
+	log     :: testing.log
+} else {
+	expect  :: proc(t: ^testing.T, condition: bool, message: string, loc := #caller_location) {
+		fmt.printf("[%v] ", loc)
+		TEST_count += 1
+		if !condition {
+			TEST_fail += 1
+			fmt.println(message)
+			return
+		}
+		fmt.println(" PASS")
+	}
+	log     :: proc(t: ^testing.T, v: any, loc := #caller_location) {
+		fmt.printf("[%v] ", loc)
+		fmt.printf("log: %v\n", v)
+	}
+}
+
+main :: proc() {
+	t := testing.T{}
+	
+	parse_json(&t)
+	marshal_json(&t)
+
+	fmt.printf("%v/%v tests successful.\n", TEST_count - TEST_fail, TEST_count)
+}
+
+@test
+parse_json :: proc(t: ^testing.T) {
+   
+	json_data := `
+	{
+	  "firstName": "John",
+	  "lastName": "Smith",
+	  "isAlive": true,
+	  "age": 27,
+	  "address": {
+		"streetAddress": "21 2nd Street",
+		"city": "New York",
+		"state": "NY",
+		"postalCode": "10021-3100"
+	  },
+	  "phoneNumbers": [
+		{
+		  "type": "home",
+		  "number": "212 555-1234"
+		},
+		{
+		  "type": "office",
+		  "number": "646 555-4567"
+		}
+	  ],
+	  "children": [],
+	  "spouse": null
+	}
+	`
+   
+	_, err := json.parse(transmute([]u8)json_data)
+
+	expect(t, err == .None, "expected json error to be none")
+}
+
+@test
+marshal_json :: proc(t: ^testing.T) {
+   
+	My_Struct :: struct {
+		a: int,
+		b: int,
+	}
+   
+	my_struct := My_Struct {
+		a = 2,
+		b = 5,
+	}
+   
+	_, err := json.marshal(my_struct)
+	
+	expect(t, err == .None, "expected json error to be none")
+}