Add libmodbus library

I used the current version found in package feed, upgraded to the latest
stable upstream version, fixed the download url and added me as maintainer.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>

libs/libmodbus/Makefile

@@ -0,0 +1,51 @@
+#
+# Copyright (C) 2006-2014 OpenWrt.org
+#
+# This is free software, licensed under the GNU General Public License v2.
+# See /LICENSE for more information.
+#
+
+include $(TOPDIR)/rules.mk
+
+PKG_NAME:=libmodbus
+PKG_VERSION:=3.0.6
+PKG_RELEASE:=1
+
+PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
+PKG_SOURCE_URL:=http://libmodbus.org/releases
+PKG_MD5SUM:=c80f88b6ca19cabc4ceffc195ca07771
+
+PKG_FIXUP:=autoreconf
+PKG_INSTALL:=1
+
+include $(INCLUDE_DIR)/package.mk
+
+define Package/libmodbus
+  SECTION:=libs
+  CATEGORY:=Libraries
+  URL:=http://www.libmodbus.org
+  TITLE:=libmodbus
+  MAINTAINER:=Michael Heimpold <mhei@heimpold.de>
+endef
+
+define Package/libmodbus/description
+A Modbus library for Linux, Mac OS X, FreeBSD, QNX and Win32
+endef
+
+TARGET_CFLAGS += $(FPIC)
+
+define Build/InstallDev
+	$(INSTALL_DIR) $(1)/usr/include
+	$(CP) $(PKG_INSTALL_DIR)/usr/include/modbus $(1)/usr/include/
+	$(INSTALL_DIR) $(1)/usr/lib
+	$(CP) $(PKG_INSTALL_DIR)/usr/lib/libmodbus.{so*,la} $(1)/usr/lib/
+	$(INSTALL_DIR) $(1)/usr/lib/pkgconfig
+	$(CP) $(PKG_INSTALL_DIR)/usr/lib/pkgconfig/libmodbus.pc $(1)/usr/lib/pkgconfig/
+endef
+
+define Package/libmodbus/install
+	$(INSTALL_DIR) $(1)/usr/lib
+	$(CP) $(PKG_INSTALL_DIR)/usr/lib/libmodbus.so* $(1)/usr/lib/
+endef
+
+$(eval $(call BuildPackage,libmodbus))