Keymap: add sun_usb keymap for sigma (#4138)

Also add users/sigma, which contains useful code for keymaps.

users/sigma/sigma.h

@@ -0,0 +1,58 @@
+/*
+  Copyright 2018 Yann Hodique <yann.hodique@gmail.com> @sigma
+
+  This program is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 2 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+#pragma once
+
+#include "quantum.h"
+#include "version.h"
+#include "eeprom.h"
+
+// Define os types
+enum os_types
+  {
+   _OS_MACOS = 0,
+   _OS_LINUX,
+   _OS_WINDOWS,
+  };
+
+// Define layer names
+enum userspace_layers
+  {
+   _QWERTY = 0,
+  };
+
+typedef union {
+  uint32_t raw;
+  struct {
+    uint8_t os_target :2;
+  };
+} userspace_config_t;
+
+enum userspace_custom_keycodes
+  {
+   EPRM = SAFE_RANGE, // Resets EEPROM
+   VRSN,              // Prints QMK Firmware and board info
+   KC_QWERTY,         // Sets default layer to QWERTY
+   KC_MAKE,           // Rebuild the current firmware
+   KC_OS_CUT,
+   KC_OS_COPY,
+   KC_OS_PASTE,
+   KC_OS_UNDO,
+   KC_OS_REDO,
+   KC_OS_LOCK,
+   KC_SCRT,
+   NEW_SAFE_RANGE     //use NEW_SAFE_RANGE for keymap specific codes
+  };