Added build to travis to verify

Closes #5466

Fine: "struct hello *world"

Not fine: "struct hello* world" (and variations)

Closes #5386

This is the common pattern used in the code and by a unified approach we
avoid mistakes.

Closes #4534

Closes #4289

It was used (intended) to pass in the size of the 'socks' array that is
also passed to these functions, but was rarely actually checked/used and
the array is defined to a fixed size of MAX_SOCKSPEREASYHANDLE entries
that should be used instead.

Closes #4169

There were a leftover few prototypes of Curl_ functions that we used to
export but no longer do, this removes those prototypes and cleans up any
comments still referring to them.

Curl_write32_le(), Curl_strcpy_url(), Curl_strlen_url(), Curl_up_free()
Curl_concat_url(), Curl_detach_connnection(), Curl_http_setup_conn()
were made static in 05b100aee247bb9bec8e9a1b0166496aa4248d1c.
Curl_http_perhapsrewind() made static in 574aecee208f79d391f10d57520b3.

For the remainder, I didn't trawl the Git logs hard enough to capture
their exact time of deletion, but they were all gone: Curl_splayprint(),
Curl_http2_send_request(), Curl_global_host_cache_dtor(),
Curl_scan_cache_used(), Curl_hostcache_destroy(), Curl_second_connect(),
Curl_http_auth_stage() and Curl_close_connections().

Closes #4096
Reviewed-by: Daniel Stenberg <daniel@haxx.se>

As previously planned and documented in DEPRECATE.md, all pipelining
code is removed.

Closes #3651

We use "conn" everywhere to be a pointer to the connection.

Introduces two functions that "attaches" and "detaches" the connection
to and from the transfer.

Going forward, we should favour using "data->conn" (since a transfer
always only has a single connection or none at all) to "conn->data"
(since a connection can have none, one or many transfers associated with
it and updating conn->data to be correct is error prone and a frequent
reason for internal issues).

Closes #3442

... by making the converter function global and accessible.

Closes #3153