Update release-notes.md to 1.5.1

Released 1.5.0

Generated documentation for 1.4.0

Generated documentation for release 1.3.10

Fixed typo in release notes

Fix minor issues in user-guide and release notes (2nd try)

Generated documentation for release 1.3.7

Generate documentation for release 1.3.6

Generated documentation for 1.3.5

Minor fix in user guide