Wrap API https request in new apiCall method

Also added: timeout and userAgent slots in KorAPConnection and output of error and warning messages.

Change-Id: I76159941a9fc56d31a560b84cc295419f52c3503
diff --git a/man/KorAPConnection-class.Rd b/man/KorAPConnection-class.Rd
index 54f6468..7f0e664 100644
--- a/man/KorAPConnection-class.Rd
+++ b/man/KorAPConnection-class.Rd
@@ -5,12 +5,17 @@
 \alias{KorAPConnection-class}
 \alias{KorAPConnection}
 \alias{initialize,KorAPConnection-method}
+\alias{apiCall,KorAPConnection-method}
+\alias{apiCall}
 \alias{show,KorAPConnection-method}
 \title{Class KorAPConnection}
 \usage{
 \S4method{initialize}{KorAPConnection}(.Object,
   KorAPUrl = "https://korap.ids-mannheim.de/", apiVersion = "v1.0",
-  apiUrl, verbose = FALSE)
+  apiUrl, userAgent = "R-KorAP-Client", timeout = 10,
+  verbose = FALSE)
+
+\S4method{apiCall}{KorAPConnection}(kco, url)
 
 \S4method{show}{KorAPConnection}(object)
 }
@@ -23,8 +28,16 @@
 
 \item{apiUrl}{URL of the KorAP web service.}
 
+\item{userAgent}{user agent string.}
+
+\item{timeout}{time out in seconds.}
+
 \item{verbose}{logical decides wether following operations will default to be verbose}
 
+\item{kco}{KorAPConnection object}
+
+\item{url}{request url}
+
 \item{object}{KorAPConnection object}
 }
 \value{