* Implement dial, support IPv6 in httpclient
Added ``dial`` procedure to networking modules: ``net``, ``asyncdispatch``,
``asyncnet``. It merges socket creation, address resolution, and connection
into single step. When using ``dial``, you don't have to worry about
IPv4 vs IPv6 problem.
Fixed addrInfo loop in connect to behave properly.
Previously it would stop on first non-immediate failure, instead of
continuing and trying the remaining addresses.
Fixed newAsyncNativeSocket to raise proper error if socket creation
fails.
Fixes: #3811
* Check domain during connect() only on non-Windows
This is how it was in the previous implementation of connect().
* Call 'osLastError' before 'close' in net.dial
* Record osLastError before freeAddrInfo in net.dial
* Add missing docs for 'dial' proc
* Optimize dial to create one FD per domain, add tests
And make async IPv6 servers work on Windows.
* Add IPv6 test to uri module
* Fix getAddrString error handling
i struggled to figure out how to post json content with nim's http client. this is a fundamental capability in many web apps, we don't always need to send data as multipart form data (e.g. when communicating via json apis) so frankly i'm surprised it isn't part of the "post" and "postContent" procs
* Adds ability to query HttpCode and compare it with strings.
* Moves HttpMethod to HttpCore module.
* Implements synchronous HttpClient using {.multisync.}.
When using `httpclient`, viewing HTTP headers is impossible without importing `strtabs`, which is very much _not_ obvious; it's impossible to know without deep diving into the docs.
Dealing with headers is an essential part of working with HTTP in general, so I propose this change. The situation is analogous to this one with `nre` and `options`: https://github.com/nim-lang/Nim/issues/4158
