- also update two URLs outside of docs/examples
- fix spelling of filename persistant.c
- fix three long lines that started failing checksrc.pl

Closes https://github.com/curl/curl/pull/3036

This example was changed in ce2140a8c1 to use the new microsecond based
getinfo option. This change makes it conditionally keep using the older
option so that the example still builds with older libcurl versions.

Closes #2584

Provide a set of new timers that return the time intervals using integer
number of microseconds instead of floats.

The new info names are as following:

CURLINFO_APPCONNECT_TIME_T
CURLINFO_CONNECT_TIME_T
CURLINFO_NAMELOOKUP_TIME_T
CURLINFO_PRETRANSFER_TIME_T
CURLINFO_REDIRECT_TIME_T
CURLINFO_STARTTRANSFER_TIME_T
CURLINFO_TOTAL_TIME_T

Closes #2495

CURLOPT_XFERINFOFUNCTION is now the preferred progress callback function
and CURLOPT_PROGRESSFUNCTION is considered deprecated.

This new callback uses pure 'curl_off_t' arguments to pass on full
resolution sizes. It otherwise retains the same characteristics: the
same call rate, the same meanings for the arguments and the return code
is used the same way.

The progressfunc.c example is updated to show how to use the new
callback for newer libcurls while supporting the older one if built with
an older libcurl or even built with a newer libcurl while running with
an older.

Adds a timer based off of CURLINFO_TOTAL_TIME that is used to perform
certain actions after a minimum amount of time has passed using the
progress function. As a consequence the curl handle is now also passed
into the progress function. Progress example now also includes an
example of how to retreive the TOTAL_TIME and print it out.