Refactored and fixed issues with retrieving the correct error codes f…

…or PostgreSQLError in case of failures; Added two unit tests for testing PostgreSQLError and PostgresSQLStatusError. Updated package to use latest CPostgresSQL

Package.swift

@@ -1,15 +1,17 @@
 import PackageDescription
 
+let beta = Version(2,0,0, prereleaseIdentifiers: ["beta"])
+
 let package = Package(
     name: "PostgreSQL",
     dependencies: [
         // Module map for `libpq`
-        .Package(url: "https://github.com/vapor/cpostgresql.git", Version(2,0,0, prereleaseIdentifiers: ["alpha"])),
+        .Package(url: "https://github.com/vapor-community/cpostgresql.git", beta),
 
         // Data structure for converting between multiple representations
-        .Package(url: "https://github.com/vapor/node.git", Version(2,0,0, prereleaseIdentifiers: ["beta"])),
+        .Package(url: "https://github.com/vapor/node.git", beta),
 
         // Core extensions, type-aliases, and functions that facilitate common tasks
-        .Package(url: "https://github.com/vapor/core.git", Version(2,0,0, prereleaseIdentifiers: ["beta"])),
+        .Package(url: "https://github.com/vapor/core.git", beta),
     ]
 )

Sources/PostgreSQL/Connection.swift

@@ -67,7 +67,7 @@ public final class Connection: ConnInfoInitializable {
             lengths.append(Int32(bind.length))
         }
 
-        let resultPointer: Result.Pointer = PQexecParams(
+        let resultPointer: Result.Pointer? = PQexecParams(
             cConnection,
             query,
             Int32(binds.count),
@@ -94,7 +94,7 @@ public final class Connection: ConnInfoInitializable {
 
     private func validateConnection() throws {
         guard isConnected else {
-            throw PostgreSQLError(code: .connection_failure, connection: self)
+            throw PostgreSQLError(code: .connectionFailure, connection: self)
         }
     }