Less verbose program parameter setters.

In future there might be functions which take values other than GL_TRUE
and GL_FALSE and this approach would be unsustainable.

src/AbstractShaderProgram.h

@@ -181,35 +181,27 @@ class MAGNUM_EXPORT AbstractShaderProgram {
 
     protected:
         /**
-         * @brief Program parameters
+         * @brief Allow retrieving program binary
          *
-         * @see setParameter()
+         * Disabled by default.
+         * @requires_gl41 Extension @extension{ARB,get_program_binary}
+         * @note This function should be called after attachShader() calls and
+         *      before link().
          */
-        enum class Parameter: GLenum {
+        inline void setRetrievableBinary(bool enabled) {
-            /**
+            glProgramParameteri(program, GL_PROGRAM_BINARY_RETRIEVABLE_HINT, enabled ? GL_TRUE : GL_FALSE);
-             * Allow retrieving program binary. Disabled by default.
+        }
-             *
-             * @requires_gl41 Extension @extension{ARB,get_program_binary}
-             */
-            RetrievableBinary = GL_PROGRAM_BINARY_RETRIEVABLE_HINT,
-
-            /**
-             * Allow the program to be bound to individual pipeline stages.
-             * Disabled by default.
-             *
-             * @requires_gl41 Extension @extension{ARB,separate_shader_objects}
-             */
-            Separable = GL_PROGRAM_SEPARABLE
-        };
 
         /**
-         * @brief Set program parameter
+         * @brief Allow the program to be bound to individual pipeline stages
          *
+         * Disabled by default.
+         * @requires_gl41 Extension @extension{ARB,separate_shader_objects}
          * @note This function should be called after attachShader() calls and
          *      before link().
          */
-        inline void setParameter(Parameter parameter, bool value) {
+        inline void setSeparable(bool enabled) {
-            glProgramParameteri(program, static_cast<GLenum>(parameter), value ? GL_TRUE : GL_FALSE);
+            glProgramParameteri(program, GL_PROGRAM_SEPARABLE, enabled ? GL_TRUE : GL_FALSE);
         }
 
         /**