- Copy stable/10 (r259064) to releng/10.0 as part of the
10.0-RELEASE cycle.
- Update __FreeBSD_version [1]
- Set branch name to -RC1

[1] 10.0-CURRENT __FreeBSD_version value ended at '55', so
start releng/10.0 at '100' so the branch is started with
a value ending in zero.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Import libyaml as libbsdyml (private brand name)

LibYAML is a YAML 1.1 parser and emitter under MIT license which will
soon be used by the pkg boostrap (usr.bin/pkg) and bhyve

Reviewed by: roberto, antoine

Import libyaml 0.1.4 into vendor