bem/bem-core — pull request #601 by apsavin (2014-07-23 19:30:00+00:00)
Title: Improve error handling and content mode

Variant of BEMTREE error hangling
[Issue 594](https://github.com/bem/bem-core/issues/594)
so you can use:
```
block('b1').content()(function() {
return this.doAsync(function() {
return doAsyncStuff();
}).then(function (data) {
return applyCtx({
block: 'b2',
content: data,
b1Stuff: this.ctx.b1Stuff
});
}, function (err) {
return err;
}, this);;
});
```
or even:
```
block('b1').content()(function() {
return this.doAsync(oAsyncStuff()).then(function (data) {
return applyCtx({
block: 'b2',
content: data,
b1Stuff: this.ctx.b1Stuff
});
}, function (err) {
return err;
}, this);;
});
```
Some part of old doAsync logic is in content mode now. I think, it's more convenient.