Add Lentient flag that prohibits 0 hosts or multiple.

[Vizonex]

Related to #816 I'm trying to figure out how we can stop a multiple or no host request from being accepted as this is a pretty bad issue that isn't just related to aiohttp aio-libs/aiohttp#10600 but affects other users also.
I do however have a pretty good understanding of llparse's architecture since I made a parody of llparse in python as a pypi package. The only thing that really concerns me is if this will actually reject client requests that do not have a host header or have multiple of them hence this being a draft. I may wind up rewriting this all completely.

close #816

[ShogunPanda]

One nit, but the PR looks fine in general.
Just add a test and we're good to go!

[Vizonex]

@ShogunPanda I didn't think I would get back when aiohttp already patched a bug but I guess I will go forward with this :)

[Vizonex]

@ShogunPanda I'll add this in just know I don't have clang (Probably should download it to locally run llparse-fixtures). Maybe in the future llparse should look into multi-compiler support example: gcc, msvc?

For now would adding something like this in suffice?

## Multiple Host

HOST_HEADER if not set should not allow multiple headers afterwards.

```http
GET /url HTTP/1.1
host: www.python.org
host: llhttp.org```

Edit: I'll raise my concern about supporting different C compilers here: nodejs/llparse-test-fixture#27 and come up with another PR if I get the time.

[Vizonex]

I am a little confused with how to get the tests to work correctly I'll see about trying again later this week.