Make testing agnostic to native newline characters, fixes #632

This is my attempt to fix all test failures on Windows that are related to CRLF line endings.

On windows git is often configured with ```core.autocrlf = true``` so that for all files that are detected as text newlines are converted to CRLF. This can lead to trouble in combination with multiline strings as they are then compiled with CRLF. Well not always: Using interpolation with expressions surrounded with curly braces in multiline strings seems to mix in ```\n```.

All this is only related to testing. But there are further implications with newlines. For example the ```FileAndResourceDirectives``` use multiline strings to render html pages. That means that the format of the output is dependent on the platform spray was compiled on. In contrast exceptions (e.g. from ```UriParser```) are mostly seperated by ```\n```s and marshalled as such.

I've changed ```FileAndResourceDirectives``` to use the native newline consistently. Should that be hardcoded? I know that HTTP headers should be separated by CRLF but can't find any info what should be preferred in bodys with text.

This patch
- explicitly converts the newlines in all multiline strings to the expected format
- removes curly braces from multiline strings
- removes the traling newline in ```empty.pdf``` (detetcted as text by git and therefore changed)

related: #107, #663