clearify backend protocol for BOMs and non ASCII-7-bit characters

[mthiede]

BOM bytes should not count for the column index and BOM bytes shouldn't be sent in the context lines.

Each escaped non ASCII-7-bit character (byte) should probably count as 1 independently of the actual encoding (count the bytes)

Update the Protocol description

[hbragge]

Just wanted to add that currently loading the model from a file with BOM leads to a backend exception:

Model loaded (0.005994921s)
[12:52:06] DEBUG response: {"type"=>"response", "invocation_id"=>11, "problems"=>[], "total_problems"=>0}
[12:52:06] INFO request complete (0.442189841s)
/home/henri/.rvm/rubies/ruby-2.1.7/lib/ruby/2.1.0/json/common.rb:155:in parse': 757: unexpected token at '{"context":["���AUTOSAR {"," ARPackage P1 {"," "],"column":5,"type":"request","command":"content_complete","invocation_id":1' (JSON::ParserError) from /home/henri/.rvm/rubies/ruby-2.1.7/lib/ruby/2.1.0/json/common.rb:155:inparse'
from /home/henri/.rvm/rubies/ruby-2.1.7/lib/ruby/2.1.0/json/common.rb:468:in JSON' from /home/henri/work/bcdevo/priv/rtext/lib/rtext/json_interface.rb:25:injson_to_object'
from /home/henri/work/bcdevo/priv/rtext/lib/rtext/message_helper.rb:32:in extract_message' from /home/henri/work/bcdevo/priv/rtext/lib/rtext/service.rb:78:inblock in run'
from /home/henri/work/bcdevo/priv/rtext/lib/rtext/service.rb:58:in each' from /home/henri/work/bcdevo/priv/rtext/lib/rtext/service.rb:58:inrun'
from /home/henri/work/bcdevo/priv/automate/lib/esr/automate/automate-rtext-service.rb:120:in <top (required)>' from /home/henri/.rvm/rubies/ruby-2.1.7/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:inrequire'
from /home/henri/.rvm/rubies/ruby-2.1.7/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in require' from /home/henri/work/bcdevo/priv/automate-test/../automate/automate-rtext-service.rb:2:in

'