This allows the compiler to check format strings. Fix a few hard-to-analyze locations and some uncovered bugs.

#2009 I did not find any more significant issues

From https://circleci.com/gh/teeworlds/teeworlds/709: >``` >[5c5644a3][engine]: running on unix-linux-amd64 >[5c5644a3][engine]: arch is little endian >[5c5644a3][storage]: couldn't open storage.cfg >[5c5644a3][storage]: using standard paths >[5c5644a3][storage]: added path '$USERDIR' ('/root/.local/share/teeworlds') >[5c5644a3][storage]: added path '$DATADIR' ('data') >[5c5644a3][storage]: added path '$CURRENTDIR' ('/root/project/release') >[5c5644a3][storage]: added path '$APPDIR' ...

This automatically builds every revision on Windows as well, helping us catch bugs or compilation failures faster. Also add automatic dependency downloading to the CMake build on Windows, fix compiler warnings of MSVS and fix a bug uncovered by these warnings.

Hi, its me again. Clients crash when too much players are disconnecting at the same time. I managed to do this with my zombie mod, when I delete all zombies at once. I fixed that by disconnecting them one by one (tick for tick), but I think this can happen in vanilla teeworlds, too. This is maybe the same issue as issue #1070.

99843b7 Add AppVeyor CI - heinrich5991 63d1748 Add automatic dependency download to CMake for ... - heinrich5991 ea80f96 Fix client masks (C4334) - heinrich5991 553db4c Fix the rest of MSVS compiler warnings - heinrich5991 4b94271 Merge pull request #2015 from heinrich5991/pr_a... - oy

b617c8b Fix an unused variable and a signed-unsigned co... - heinrich5991 bb8ec6b Test CMake on CircleCI - heinrich5991 ce59e97 Make versionsrv's dependency on nethash.cpp exp... - heinrich5991 9bf8140 Also try running the server on CircleCI - heinrich5991 e117ee0 Recursively create directories for the data dir - heinrich5991

88a0400 Fix a few issues raised by Codacy - Dune-jr 040b02c Merge pull request #2012 from Dune-jr/codacy-fixes - oy

89295f1 Annotate dbg_msg and str_format for -Wform... - heinrich5991 [d75d453](https://github.com/teeworlds/teeworlds/commit/d75d4535ae370583956b8a149097b4f38107efdf) Remove non-constant format strings - heinrich5991 [de344ba](https://github.com/teeworlds/teeworlds/commit/de344ba221989b80438fa36e49aade1520fc323c) Fix incorrect format strings - heinrich5991 [802ecc5`](https://github.com/teeworlds/teeworlds/commit/802ecc5136878826ad162a318a8656330b8cb03e) Merge pull request #2011 from heinrich5991/pr_f... - oy

d9cf505 Refactor spec mode selection without case fallt... - heinrich5991 c21cc0a Remove last remaining case fallthrough in the c... - heinrich5991 dbf056b Simplify code using str_comp a bit - heinrich5991 3b1bea2 Merge pull request #2010 from heinrich5991/pr_f... - oy

cfbe266 Added api and UI()->IsClipped() - LordSk 1f8936a Fixed scroll not being reset when scrollbar is ... - LordSk 81efacb Reorganize piece of code - LordSk 48968fa Added a small documentation to the api - LordSk c66037a Small fix to the doc - LordSk

e5f2c4f removed duplicate code. closes #2005 - oy

6deb18e changed swap to tl_swap to prevent interference... - oy 397e88e use stable_sort for sorting - oy

6df2d43 fixed some warnings - oy

6f980c3 show AppVeyor build status in the readme - oy

e1efafc fixed last commit - oy

5b002b0 fixed some warnings - oy

f8ba164 removed old deprecated scale code - oy

• -fcf-protection to protect the targets of indirect jumps and function returns.
• -D_GLIBCXX_ASSERTIONS for bounds-check assertions in the STL.
• -fstack-clash-protection to protect against stacks overwriting each other.
• -fstack-protector-strong instead of -fstack-protector-all as it apparently gives basically the same benefits at less slowdown.

These flags were taken from https://developers.redhat.com/blog/2018/03/21/compiler-and-linker-flags-gcc/.