add `opts.compiler` allows third party to override the internal compiler
condition checking on opts.compiler is existed and is a function, and pass compilerOptions into compiler module
adding a test case for opts.compiler
update the API documentation for options.compiler
add an Handlebars Ember-HTMLbar example
Update Basic_htmlbars.js

remove the trailing space in the plain text file
update the readme documentation of how to use `options.compiler`
update the example/ember-htmlbars documentation
remove the truthy check on `compiler` and use type check only
Use offical `ember-cli-htmlbars` module in the `ember-htmlbars` example
Add the real world working example for compiling ember#1.9.0, handlebars#2.0.0, htmlbars application in examples/ember-htmlbars