add :preamble option to compiler

Description

Per this thread:

https://groups.google.com/forum/#!searchin/clojurescript/preamble/clojurescript/rUIlLfcYZvE/Yskfh4znL_0J

1) reamble 's value will be a vector of paths
2) the compiled output is prepended with the contents of the files at those paths
3) the generated source map points to the correct/adjusted line numbers

Additionally, when compiling for the :nodejs target the preamble contents will default to the hashbang we currently write in that situation.

Environment

None

Assignee

Unassigned

Reporter

Travis Vachon

Labels

Approval

None

Patch

None

Priority

Minor
Configure