Update NEWS file for v3.1.4

NEWS

@@ -1,3 +1,28 @@
+libmodbus 3.1.4 (2016-05-28)
+============================
+
+- C_PROG_RANLIB is rendered obsolete by LT_INIT
+- Improve ifdef around bswap_16 for __CYGWIN__
+- Improve Cygwin support. Thanks to StalderT.
+- Another round of DRY in modbus_reply()
+- Rename raw_rep to raw_rsp in unit-test-client
+- Fix wrong function name in debug message
+- Fix handling of invalid function code (closes #315)
+- Add debug message on unknown function and new unit test
+- DRY in modbus_reply by improving response_exception()
+- Fix typo in 3053bd0adb
+- CID 69145 - Argument cannot be negative in unit-test-server
+- CID 69142 - Unchecked return value in unit-test-server
+- Fix CID 69140 - Bad bit shift operation (coverity) in tests
+- Rewrite and rename README as README.md in tests/
+- Github's contributing and issue template files
+- Fix small leak (64 bytes in TCP) in unit-test-client
+- Add unit-tests.sh to tarball
+- Add ./configure.scan to .gitignore
+- Move setting of option inside the relevant conditional group
+- Add links to new modbus_*_float_* functions in index
+- Slight change to modbus_report_slave_id doc.
+
 libmodbus 3.1.3 (2016-05-11)
 ============================