Allow string return type, and URL-encode param (#38)

MyriadPlugin.Test/TestPathParam.fs

@@ -0,0 +1,36 @@
+namespace MyriadPlugin.Test
+
+open System
+open System.Net
+open System.Net.Http
+open NUnit.Framework
+open FsUnitTyped
+open PureGym
+
+[<TestFixture>]
+module TestPathParam =
+
+    [<Test>]
+    let ``Path params are escaped`` () =
+        let proc (message : HttpRequestMessage) : HttpResponseMessage Async =
+            async {
+                message.Method |> shouldEqual HttpMethod.Get
+
+                let expectedUriPrefix = "https://example.com/endpoint/"
+
+                let actualUri = message.RequestUri.ToString ()
+
+                if not (actualUri.StartsWith (expectedUriPrefix, StringComparison.Ordinal)) then
+                    failwith $"wrong prefix on %s{actualUri}"
+
+                let content = new StringContent (actualUri.Substring expectedUriPrefix.Length)
+                let resp = new HttpResponseMessage (HttpStatusCode.OK)
+                resp.Content <- content
+                return resp
+            }
+
+        use client = HttpClientMock.make (Uri "https://example.com") proc
+        let api = PureGymApi.make client
+
+        api.GetPathParam("hello/world?(hi)").Result
+        |> shouldEqual "hello%2fworld%3f(hi)"