Support multipart/form-data

Add multipart/form-data support and testing support
Add substream for seekable streams
implement IPostedFile in NativeMiddleware.FormSupport
Organize extension methods
do better async Stream extension methods
add Task extension methods
Organize ReSharper Settings
Move DumpContent to NativeMiddleware
Merge pull request #22 from EddieGarmon/issue-3-FileUpload

add support for multipart/form-data and file uploads