Userland: Add support for jails

This happens in two ways:
1. LibCore now has two new methods for creating Jails and attaching
   processes to a Jail.
2. We introduce 3 new utilities - lsjails, jail-create and jails-attach,
   which list jails, create jails and attach processes to a Jail,
   respectively.

Base/usr/share/man/man1/jail-attach.md

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+## Name
+
+jail-attach - attach a new process to existing jail
+
+## Synopsis
+
+```**sh
+$ jail-attach <jail index> <command>
+```
+
+## Description
+
+`jail-attach` attaches a new process by specifying a command, to an existing jail, with a
+specified jail index.
+
+## Examples
+
+```sh
+# Attach the command "ps -ef" to a jail with the index 0
+$ jail-attach 0 ps -ef
+```

Base/usr/share/man/man1/jail-create.md

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+## Name
+
+jail-create - create a new jail
+
+## Synopsis
+
+```**sh
+$ jail-create <name>
+```
+
+## Description
+
+`jail-create` creates a new jail, with a specified name
+
+## Examples
+
+```sh
+# Create jail with the name "test-jail"
+$ jail-create test-jail
+```

Base/usr/share/man/man1/lsjails.md

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+## Name
+
+lsjails - list existing jails
+
+## Synopsis
+
+```**sh
+# lsjails
+```
+
+## Description
+
+This utility will list all existing jails at the moment of invoking this program.
+Please note that if the current process is in jail, it will not see any jail.
+
+## Examples
+
+```sh
+# lsjails
+Index   Name
+2       test-jail
+```