c-ares version 1.15.0

Changes:
 o Add ares_init_options() configurability for path to resolv.conf file [1]
 o Ability to exclude building of tools (adig, ahost, acountry) in CMake [3]
 o Android: Support for domain search suffix [4]
 o Report ARES_ENOTFOUND for .onion domain names as per RFC7686. [13]

Bug fixes:
 o AIX build fix for trying to include both nameser_compat.h and
   onameser_compat.h [2]
 o Windows: Improve DNS suffixes extracting from WinNT registry [5]
 o Fix modern GCC warnings [6]
 o Apply the IPv6 server blacklist to all nameserver sources, not just Windows
   [7]
 o Fix warnings emitted by MSVC when using -W4 [8]
 o Prevent changing name servers while queries are outstanding [9]
 o Harden and rationalize c-ares timeout computation [10]
 o Distribute ares_android.h [11]
 o ares_set_servers_csv() on failure should not leave channel in a bad state
   [12]
 o Add missing docs to distribution

Thanks go to these friendly people for their efforts and contributions:
  @afalin, Andi Schnebinger, Ben Noordhuis, Brad House, Brad Spencer,
  David Hotham, @flyingdutchman23, John Schember, Ruslan Baratov,
  Sarat Addepalli, Tobias Nießen (11 contributors)

References to bug reports and discussions on issues:
 [1] = https://github.com/c-ares/c-ares/issues/220
 [2] = https://github.com/c-ares/c-ares/issues/224
 [3] = https://github.com/c-ares/c-ares/issues/200
 [4] = https://github.com/c-ares/c-ares/issues/207
 [5] = https://github.com/c-ares/c-ares/pull/202
 [6] = https://github.com/c-ares/c-ares/pull/201
 [7] = https://github.com/c-ares/c-ares/pull/193
 [8] = https://github.com/c-ares/c-ares/pull/192
 [9] = https://github.com/c-ares/c-ares/pull/191
 [10] = https://github.com/c-ares/c-ares/pull/187
 [11] = https://c-ares.haxx.se/mail/c-ares-archive-2018-04/0000.shtml
 [12] = https://c-ares.haxx.se/mail/c-ares-archive-2018-03/0000.shtml
 [13] = https://github.com/c-ares/c-ares/issues/196