Combine TSParser and TSStateMachine objects

My original thought was to decouple the runtime from
the LR parser generator by making TSParser a generic
interface that LR parsers implement.

I think this was more trouble than it was worth.

spec/runtime/document_spec.cc

@@ -0,0 +1,78 @@
+#include "runtime/runtime_spec_helper.h"
+#include "runtime/helpers/spy_reader.h"
+
+extern "C" TSParser * ts_parser_json();
+
+START_TEST
+
+describe("incremental parsing", [&]() {
+    TSDocument *doc;
+    SpyReader *reader;
+
+    before_each([&]() {
+        doc = ts_document_make();
+        ts_document_set_parser(doc, ts_parser_json());
+
+        reader = new SpyReader("{ \"key\": [1, 2] }", 5);
+        ts_document_set_input(doc, reader->input);
+    });
+
+    after_each([&]() {
+        ts_document_free(doc);
+        delete reader;
+    });
+
+    it("parses the input", [&]() {
+        AssertThat(string(ts_document_string(doc)), Equals(
+            "(value (object (string) (array (number) (number))))"));
+    });
+
+    it("reads the entire input", [&]() {
+        AssertThat(reader->strings_read, Equals(vector<string>({
+            "{ \"key\": [1, 2] }"
+        })));
+    });
+
+    describe("modifying the end of the input", [&]() {
+        before_each([&]() {
+            size_t position(string("{ \"key\": [1, 2]").length());
+            string inserted_text(", \"key2\": 4");
+
+            reader->content.insert(position, inserted_text);
+            ts_document_edit(doc, { position, 0, inserted_text.length() });
+        });
+
+        it("updates the parse tree", [&]() {
+            AssertThat(string(ts_document_string(doc)), Equals(
+                "(value (object (string) (array (number) (number)) (string) (number)))"));
+        });
+
+        it("re-reads only the changed portion of the input", [&]() {
+            AssertThat(reader->strings_read.size(), Equals<size_t>(2));
+            AssertThat(reader->strings_read[1], Equals(", \"key2\": 4 }"));
+        });
+    });
+
+    describe("modifying the beginning of the input", [&]() {
+        before_each([&]() {
+            size_t position(string("{ ").length());
+            string inserted_text("\"key2\": 4, ");
+
+            reader->content.insert(position, inserted_text);
+            ts_document_edit(doc, { position, 0, inserted_text.length() });
+        });
+
+        it("2 updates the parse tree", [&]() {
+            AssertThat(string(ts_document_string(doc)), Equals(
+                "(value (object (string) (number) (string) (array (number) (number))))"));
+        });
+
+        it_skip("re-reads only the changed portion of the input", [&]() {
+            AssertThat(reader->strings_read.size(), Equals<size_t>(2));
+            AssertThat(reader->strings_read[1], Equals("\"key2\": 4, "));
+        });
+    });
+
+});
+
+END_TEST