example, Body type, cast

added example, exception handling around httpwebrequest cast and changed
request / response body to body because the type is the same and it is
shorter
body du's, function name, bodyvalues gone

removed bodyvalues
added ReqBody and ResBody DU
changed RequestDetailed to Request
and Request to RequestString
Some updates to the documentation.
rename + default content types

res _> response
req -> request
default content types text -> text/plain, binary ->
application/octet-stream, values -> application/x-www-form-urlencoded