Rename SAMD directories and configuration variables to SAMDL so that the same build environment can support the SAML

Clean up some logic in the CDC/ACM host drivers.  Test with some other host controller drivers.  There are lots of problems.

Re-implemened pthread_kill().  It as just a simple wrapper around kill() but since the correct dispatching of singles for multi-threaded task groups has been implemented, calling kill() does no work.  The corrected implementation of pthread_kill() will direct the signal specifically to the specific pthread and no other.

SAMV71-XULT: Reads from LCD memory do not work.  Change configuration so that the LCD is treated as write-only

Add inclusion of assert.h in networking files where needed to avoid compilation errors.  From Max Neklyudov.

SAMV7 TWIHS:  Fix logic that performs multi-message tranfers with and without repeated starts.  This change is the final piece that was required to get the maXTouch Xplained Pro workding.

USB device.  All class drivers.  There needs to be a check to make sure that the size of a returned string does not exceed the size of an allocated request buffer

Local sockets: Local stream sockets had problem of double releasing pipes (both server and client attempt release), which causes wrong pipe pair being closed in multi-client case. Solve by adding per connection instance ID to pipe names.  From  Jussi Kivilinna (2015-05-12).