NEWS.md: Adjust further for release

Regen strings

Merge pull request bcpierce00#608 from gdt/master

Update version/NEWS for 2.51.5

regen NEWS

Merge pull request bcpierce00#400 from glondu/fix-custom

Put -custom in CAMLLIBS instead of CAMLFLAGS

Merge pull request bcpierce00#136 from bcpierce00/beta-release

Bits of tidying during release

Add -unsafe-string switch, for compatibility with OCaml >=4.06

no longer generate Makefile.ProjectInfo

Merge pull request bcpierce00#107 from bcpierce00/beta-release-prep

Beta release prep

fix to compile with newer caml