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.

src/runtime/lexer.c

@@ -0,0 +1,43 @@
+#include "tree_sitter/runtime.h"
+#include "tree_sitter/parser.h"
+
+TSLexer ts_lexer_make() {
+    return (TSLexer) {
+        .chunk = NULL,
+        .debug = 0,
+        .chunk_start = 0,
+        .chunk_size = 0,
+        .position_in_chunk = 0,
+        .token_start_position = 0,
+        .token_end_position = 0,
+        .reached_end = 0
+    };
+}
+
+int ts_lexer_advance(TSLexer *lexer) {
+    static const char *empty_chunk = "";
+    if (lexer->position_in_chunk + 1 < lexer->chunk_size) {
+        lexer->position_in_chunk++;
+    } else {
+        lexer->chunk_start += lexer->chunk_size;
+        lexer->chunk = lexer->input.read_fn(lexer->input.data, &lexer->chunk_size);
+        lexer->position_in_chunk = 0;
+        if (lexer->reached_end) {
+            return 0;
+        }
+        if (lexer->chunk_size == 0) {
+            lexer->reached_end = 1;
+            lexer->chunk = empty_chunk;
+        }
+    }
+    return 1;
+}
+
+TSTree * ts_lexer_build_node(TSLexer *lexer, TSSymbol symbol) {
+    size_t current_position = ts_lexer_position(lexer);
+    size_t size = current_position - lexer->token_start_position;
+    size_t offset = lexer->token_start_position - lexer->token_end_position;
+    lexer->token_end_position = current_position;
+    return ts_tree_make_leaf(symbol, size, offset);
+}
+