add html utf8 bom signature

[napalu]

closes #267

[coveralls]

Coverage remained the same at 96.407% when pulling b0140e7 on napalu:bugfix/html_utf8_bom into 71f0e2b on gabriel-vasile:master.

[gabriel-vasile]

Hi and thank you for your contribution.
There is a problem with current solution: it does not work when there is whitespace between BOM and HTML signature.
I added a testcase to show the problem.

I think a solution for this would be to trim the BOM here, before the trimLWS call. Let me know if you other idea how to do it.

[napalu]

Hi and thank you for your contribution. There is a problem with current solution: it does not work when there is whitespace between BOM and HTML signature. I added a testcase to show the problem.

Hi - good catch - I'll have a look at it tomorrow and update the PR.

[napalu]

@gabriel-vasile I think your proposal of trimming the BOM before trimLWS is good - I chose to skip and then restore it after stripping so its presence can be used later on if needed.

[gabriel-vasile]

Hi, I'm not sure I understand the reason for restoring the BOM. The way I see it, trimming the BOM will always be more efficient and still detect MIME type correctly.

[gabriel-vasile]

Hi, the code looks all good. Just one small issue with comments to solve before I can merge.