Update CHANGELOG and VERSION

CHANGELOG.md

 Changelog
 =========
 
-v5.1.0
-------
-**Library**
-- Added IMEXOrder4, RK5 and AB4 time integration schemes (!1037)
-
-**FieldConvert**
-- Add field conversion from Halfmode to SingleMode (!1032)
-
 v5.0.0
 ------
 **Library**
@@ -85,6 +77,7 @@ v5.0.0
 - Added flag to skip periodic BCs while filling Dirichlet BCs in
   ContField3D.cpp (!1018)
 - Fix bounding box for interpolation (!1033)
+- Added IMEXOrder4, RK5 and AB4 time integration schemes (!1037)
 
 **NekMesh**:
 - Add feature to read basic 2D geo files as CAD (!731)
@@ -145,6 +138,7 @@ v5.0.0
 - Added if statement to fix case of 1D/2D manifold interpolation in 1D/2D space,
   added check on dimensions for interpolation, fixed seg interp (!999)
 - Fixed scaling for compressed xml, fixed error printout for mesh only (!1040)
+- Add field conversion from Halfmode to SingleMode (!1032)
 
 **IncNavierStokesSolver**
 - Replace steady-state check based on difference of norms by check based on

VERSION

-5.0.0b
+5.0.0