Stack traces could be better in general

[arggh]

Is your feature request related to a problem? Please describe.
Would be nice to have better stack traces and error messages.

One of my components was using document outside of onmount.

This is was not as helpful, as it could have been:

ReferenceError: document is not defined
    at create_ssr_component (/Users/arggh/app/__sapper__/dev/server/server.js:4733:11)
    at Object.$$render (/Users/arggh/app/__sapper__/dev/server/server.js:265:22)
    at create_ssr_component (/Users/arggh/app/__sapper__/dev/server/server.js:4772:59)
    at Object.$$render (/Users/arggh/app/__sapper__/dev/server/server.js:265:22)
    at create_ssr_component (/Users/arggh/app/__sapper__/dev/server/server.js:4958:41)
    at $$render (/Users/arggh/app/__sapper__/dev/server/server.js:265:22)
    at Object.render (/Users/arggh/app/__sapper__/dev/server/server.js:273:26)
    at handle_page (/Users/arggh/app/__sapper__/dev/server/server.js:7336:36)
    at <anonymous>

Describe the solution you'd like
I'd like to know where things are not working without combing through 50k lines of server.js, maybe even accompanied by a helpful message describing why it's not working and what should be done.

How important is this feature to you?
It's not a show stopper, but it sure does make Sapper feel unfinished and takes a toll on developer experience and productivity.

[benmccann]

There's a PR for this: #773

[benmccann]

This should be fixed when Sapper 0.28.1 is released