Bump to v5.1.0-rc1+dev91 and update README

Integration Candidate 2020-11-24

README.md

@@ -10,6 +10,16 @@ The autogenerated OSAL user's guide can be viewed at <https://github.com/nasa/cF
 
 ## Version History
 
+### Development Build: 5.1.0-rc1+dev91
+
+- Rename `UT_SetForceFail` to `UT_SetDefaultReturnValue` since some functions that retain more than 1 value are not necessarily failing
+- Add a 5th timer to TimerTest functional to test the one shot (zero-length time interval) case.
+- Ensure all APIs use the proper type. Sizes are now size_t; these will now be 64 bits on a 64 bit platform.
+- Fix build issue on VxWorks 6.9 by using the 3 argument form of `open()`. Passing `0` as the mode solves the build issue. This parameter is ignored when not creating a file.
+-  The address calculations now use `unsigned long` instead of `long` to ensure that all rounding and base address adjustments behave the same way in the event that the addresses lie in the upper half of memory (i.e. start with a 1 bit) which would put it in the negative range of a long type.
+- See <https://github.com/nasa/osal/pull/662>
+
+
 ### Development Build: 5.1.0-rc1+dev75
 
 - Ensure that the handle is not NULL before invoking dlclose(). In particular the handle will be NULL for static modules. Shutdown after CTRL+C occurs normally (no segfault).

src/os/inc/osapi-version.h

@@ -30,7 +30,7 @@
 /*
  * Development Build Macro Definitions
  */
-#define OS_BUILD_NUMBER   75
+#define OS_BUILD_NUMBER   91
 #define OS_BUILD_BASELINE "v5.1.0-rc1"
 
 /*