(feat) added a simple StringWriter to bridging writer based API and original String based API.
(feat) added a simple StringWriter to bridging writer based API and
original String based API.

tempbottle/handlebars-rust,sunng87/handlebars-rust,wang19742008/handlebars-rust,sunng87/handlebars-rust,tailhook/handlebars-rust,ihrwein/handlebars-rust,tempbottle/handlebars-rust,tailhook/handlebars-rust