Restructuring code w.r.t. configurations and definitions:
- #defines have been mostly removed from configurations
- a dedicated config file has been added for configurations with constexpr
- past configure file is now only a cmake wrapper
- wrapping global functions into namespaces

Removed all adafs and ifs occurrences. Now called gkfs

Fixes #74.

Closes #73

Fixes #65.

Fixes #64.

Fixes #63.

Fixes #47

CREATE_CHECK_PARENTS controls if the existance of the parent node needs
to be checked during the creation of a child node.

Example: The check prevents the creation of file `/parent/child`
if `/parent` doesn't exists or if it is not a directory

By default CREATE_CHECK_PARENTS is enable and the check is enforced.
It can be disable to speedup creation operations by passing
`-DCREATE_CHECK_PARENTS:BOOL=OFF` as cmake parameter.

All paths underl /sys and /proc are forwarded to the kernel directly

Fixes an issue where client applications such as ssh might attempt to
close all open fds, therefore also closing the fds used by the internal
components of the library such as Mercury.