[transport] detect and warn about unaligned esc sequences

[r00t-]

first step of improvement towards #103 (see also devZer0/libsml-testing#12 )

this at least provides a warning:

$ ./examples/sml_server - <libsml-testing/EasyMeter_Q3A_A1064V1009.bin  >/dev/null 
libsml: warning: could not read the whole file
libsml: warning: unaligned end esc sequence found in data, stream desynced?
libsml: warning: unaligned (likely) start esc sequence found in data, stream desynced?
libsml: warning: unaligned end esc sequence found in data, stream desynced?
libsml: warning: unaligned (likely) start esc sequence found in data, stream desynced?
libsml: warning: unaligned end esc sequence found in data, stream desynced?
libsml: warning: unaligned (likely) start esc sequence found in data, stream desynced?
libsml: warning: unaligned end esc sequence found in data, stream desynced?
libsml: warning: unaligned (likely) start esc sequence found in data, stream desynced?

[r00t-]

this could be merged as-is, but it would heavily spam a user's log in case of a desync.
(might still be better than silently stopping to return data.)
we should extend it to re-sync to the data stream somehow.

[r00t-]

(also the code is rather simplistic and inefficient, there should be better ways to do this.)