Support agile extension of Eta class (#249)

src/compile-string.ts

@@ -14,6 +14,8 @@ export function compileToString(this: Eta, str: string, options?: Partial<Option
   const config = this.config;
   const isAsync = options && options.async;
 
+  const compileBody = this.compileBody;
+
   const buffer: Array<AstObject> = this.parse.call(this, str);
 
   // note: when the include function passes through options, the only parameter that matters is the filepath parameter
@@ -72,7 +74,7 @@ return __eta.res;
  * ```
  */
 
-function compileBody(this: Eta, buff: Array<AstObject>) {
+export function compileBody(this: Eta, buff: Array<AstObject>) {
   const config = this.config;
 
   let i = 0;

src/core.ts

@@ -1,6 +1,6 @@
 import { Cacher } from "./storage.ts";
 import { compile } from "./compile.ts";
-import { compileToString } from "./compile-string.ts";
+import { compileToString, compileBody } from "./compile-string.ts";
 import { defaultConfig } from "./config.ts";
 import { parse } from "./parse.ts";
 import { render, renderAsync, renderString, renderStringAsync } from "./render.ts";
@@ -26,6 +26,7 @@ export class Eta {
 
   compile = compile;
   compileToString = compileToString;
+  compileBody = compileBody;
   parse = parse;
   render = render;
   renderAsync = renderAsync;