fix: use std::result::Result instead of Result in handlebar_helper!()…

… macro

It is often customary to define crate wide Error and Result type.
Something like:

type Error = ...
type Result<T> = std::result::Result<T, Error>

If such Result<T> type is in scope when calling the handlebar_helper!()
macro, compilation fails as the number of template argument is not the
same.

This commit modified macro to rely explicitely on std::result::Result<>
instead of the whatever Result type is in scope when the macro is
invoked.

src/macros.rs

@@ -54,7 +54,7 @@ macro_rules! handlebars_helper {
                 r: &'reg $crate::Handlebars<'reg>,
                 _: &'rc $crate::Context,
                 _: &mut $crate::RenderContext<'reg, 'rc>,
-            ) -> Result<$crate::ScopedJson<'rc>, $crate::RenderError> {
+            ) -> std::result::Result<$crate::ScopedJson<'rc>, $crate::RenderError> {
                 let mut param_idx = 0;
 
                 $(