Run goimports manually since returns.Process does not.

/cc @sqs It would make more sense and be better API to have the library
do everything inside returns.Process, rather than having goimports
functionality only in goreturns binary.
Clean up legacy stateless print funcs.

This reduces code duplication.
Use factored out markdown_http.MarkdownHandlerFunc.
Don't panic on WriteFile error (e.g., permission denied).
Add adjustable texture LOD bias parameter to debug panel.
Make mode into a flag rather than const.
Add Ctrl+G shortcut for Go To Line.