git: ignore sample executable
l2cap: remove unnecessary type conversion
l2cap: return validated c.mtu

Make sure the value fits a reasonable range.
notifier: extract notifier code to a separate file
server: remove singleton constraint from Server for now

We could have multiple instances (one instance per HCI
device).  Associate the serving status on per-server
basis instead.
conn: move conn code to a separate file
Remove l2capHandler

This PR aims to replace the c-shim with a pure go implementation
hci subpackage. However, it is not a drop-in replacement, and
will have a very large diffs. Along with the series of commits,
we'll blur the boundary between existing data structures as well
as files. Keep moving generic (non-c-shim specific) code to
individual files, and make it platform independent as possible.

At the end of the migration, the diff should be confined in
certain files or data structures.
Move gatt handling code from l2cap to conn

pure code movement
Migrate gatt handling code from l2cap to conn
Decouple l2cap and conn(gatt handling) with io.ReadWriteCloser

This is a stepstone for switching from c-him to go-hci.
We'll be back to rework this snippet to either conform the
io.ReadWriteCloser semantic or cook another interface
between L2CAP.
Move gatt handling code from server to conn

pure code movement
Migrate gatt handling code from server to conn
Move notifier from characteristic to conn
Move handles from l2cap to server
Move *conn related code from server to l2cap

pure code movement
Migrate *conn related code from server to l2cap
linux: initial import of linux sub-package
Migrate from c-shim to go-hci

The diff looks large, as the go-hci is not a pin-to-pin drop-in
replacement of the c-shim. However, the rewritten files are actually
pretty small.

We've been re-organzing and refacoring the code base to move c-shim
specific code to l2cap.go, or leave it in server.go. So right now
at this point, the changes of migration itself actually only involves
server.go and the separate advertser.go, which were extracted from
from the server.go.

Currently, the non-c-shim branch is working fine, but still need a
lot of re-working, refactoring, and layering.
Obsolete c-shim codebase
Merge pull request #9 from roylee17/feature/go-hci-v4

Feature/go hci v4