Build fix and new timeout options

* Fix link errors that started to get triggered with new build
  toolchains.

* New timeout options:
  * `--timeout-connection-period`
  * `--timeout-low-speed-period`
  * `--timeout-low-speed`

Update build system and fix building with GCC 8.1 with -Wall -Werror

 * The way previously-shipped `waf` was checking the existence of
   functions triggers a warning/error with GCC 8.1. `waf` is now
   up-to-date. And fragments are created in `wscript` to check for
   functions properly.

 * saldl now halves chunk-size if it's between 0.5 and 1.5 of
   file-size. This is done to avoid contention in a single connection.

Bugfix: Detect "Content-Encoding: none"

* [fix] Detect non-standard "Content-Encoding: none" returned from some
  servers. This fix will not be necessary with `libcurl >= 7.59`. But
  distributions will not have that fix for some time.

New configure options/ New CLI option

 * [New] Add `./waf configure` options `--default-chunk-size` and `--default-num-connections`.
 * [New] Add CLI option `--get-info` (valid arguments are "file-name", "file-size", and "effective-url").
 * [Build] Raise minimum libcurl version required to 7.55.0.

Fix truncation options / Improve --whole-file

 * Truncation options `-t`,`--auto-trunc` and `-T`,`--smart-trunc`
   were broken in `v36`. The are fixed in this release.

 * When using `--whole-file`, it is ensured now that the no. of chunks
   (including the last one) will equal the no. of connections. That
   is, all chunks will start downloading immediately from the start.

GCC 7 build fixes

 Building saldl with GCC 7 (7.1.1 to be exact) triggers a couple of
 warnings. And since `-Werror` is passed by default (as a way to
 enforce a zero warning policy), those warnings actually  manifest
 as errors, causing builds to fail.

 This release does not contain functional changes. It only includes one
 direct, and one indirect build fixes.

Fix for OSX El Capitan, a breaking change, and a couple of new options

HIGHLIGHTS

 * [breaking] Make `-H` short for `--custom-headers` instead of `--use-HEAD`
 * [new] Add `--random-order` option
 * [new] Add `-F`/`--allow-ftp-segments` option
 * [fix] Fix OSX El Capitan builds with Xcode 8

v34: New option `--merge-in-order`, and some fixes

Compared to v33, this is a rather small release.

HIGHLIGHTS

 * [fix] Fix `-I`/`--no-remote-info`. Changes in v33 caused a crash if
   this option was passed (b8e292c).

 * [new] Implement `--merge-in-order`. This option forces merging
   chunks in order, similar to how piping to `stdout` works
   (d739fbc).

 * [change] Limit reconnection delays to 32 seconds max
   (3729b30).

Check out `git log v33..v34` for a full list of changes.

v33: `--mirror-url`, `--stdout`, and other changes and fixes

In this release, the option to download from two servers concurrently
is made possible with option `--mirror-url`. Consult the manual page
for details.

Also in this release, support for writing to stdout was added
(option `--stdout`). All saldl's optimizations will work, except
chunks will only be merged sequentially. If `-m`/`--memory-buffers`
are used, saldl will not create any files or write any data to disk.
Consult the manual page for more details.

= Other notable changes and fixes

* [fix] Handle relative redirects correctly
  (b21fbfd).

* [fix] Fatally fail with any HTTP error other than 400 while getting
  remote info. 400 is allowed once in case it was caused by an HTTP/2
  upgrade error (d88036d).

* [fix] Fix long options `--since-file-mtime` and `--date-cond`.
  They erroneously required an extra `--` at the start
  (c33187a).

* [new] Only enable HTTP/2 over TLS by default. `--http2-upgrade` to
  always try HTTP/2 [requires libcurl >= 7.47.0]
  (70892aa).

* [new] Implement `-6`/`--resolve-ipv6` and `-4`/`--resolve-ipv4`
  (128de2b).

* [new] Send TCP keep-alive probes every 6s, `--no-tcp-keep-alive` to
  disable (0bd1a51).

Check `git log v32..v33` for a full list of changes.

Major changes in compression/decompression options

Highlights

* [major] Big and breaking changes in compression/decompression options (b477928).
* [new] Implement -M/--since-file-mtime and -Y/--date-cond (3576819).
* [fix] Fall back to HTTP/1.1 if we get a 400 response. The error could
  be triggered by the HTTP/2 upgrade request (08f372c).