Replace `README.md` with a notice linking to the new location.

Add deprecation notice.

See github/smimesign#84

v0.1.0

Release notes:

- The URL has moved from github.com/mastahyeti/certstore to github.com/github/certstore .
- No code changes.

Merge pull request #12 from mastahyeti/mod

Go modules

Merge pull request #10 from mastahyeti/windows-errors

Don't rely on GetLastError always returning an error

Merge pull request #9 from mastahyeti/linux-error

More helpful compiler error on Linux

Run CI on x86 and x64. Fix some 32 bit problems.

Merge pull request #6 from mastahyeti/go-1.10.4

Remove workaround for go 1.10.0→1.10.3