added custom error classes

Added CAPI and Login custom error classes.

Cleaned up output when error is thrown.

lib/errors.ps1

@@ -0,0 +1,25 @@
+class LoginError : Exception {
+    [String]$msg
+
+    LoginError([String]$msg) {
+        $this.msg = $msg
+    }
+
+    [String] ErrorMessage() {
+        return $this.msg
+    }
+}
+
+class CAPIError : Exception {
+    [Int]$retval
+    [String]$caller
+
+    CAPIError([Int]$retval, [String]$caller) {
+        $this.retval = $retval
+        $this.caller = $caller
+    }
+
+    [String] ErrorMessage() {
+        return "ERROR: CAPI return value: {0} in {1}" -f $this.retval, $this.caller
+    }
+}