Prepare zstd for 1.5.0 release

[senhuang42]

• Bump version number
• Rebuild documentation (with make all)
• Next Step: merge dev into release after this is merged.

[Cyan4973]

Are you also able to rebuild the man pages ?
cd programs; make man

It relies on Ruby, so it's not guaranteed to work out of the box.
If not, I'll do it in a separate PR.

[senhuang42]

Are you also able to rebuild the man pages ?
cd programs; make man

It relies on Ruby, so it's not guaranteed to work out of the box.
If not, I'll do it in a separate PR.

Gah, unfortunately ruby refuses to install properly on my mac, and running make man on my devserver has no effect. Could you submit the PR for this?

[Cyan4973]

Sure, I'll follow up after this one