[plugins] director: some work on the cache subsystem
[plugins] director: use the Age response header, instead of X-Cache-Age
[base] Buffer: provide != operators
[plugins] director: drop some abstractions, but add another one (for Vary-header-support)
[http] HttpRequest: adding another helpful request-header retrieval fn
[http] HttpRequest: minor optimization

by using the right type and prevent implicit conversions.
C-API braindstorm code.
oh sh***
missing typedef
capi: update
capi: update
capi: update
capi: update
capi: update
Defines.h: make file C compatible
Defines.h: more C compatibility
capi: update + example code
capi: update
cmake: make x0d and x0d plugins optionally compilable
cmake: added ENABLE_MANPAGES [on]