Update libcurl

Engine/lib/curl/docs/VERSIONS.md

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+Version Numbers and Releases
+============================
+
+ Curl is not only curl. Curl is also libcurl. they are actually individually
+ versioned, but they usually follow each other closely.
+
+ The version numbering is always built up using the same system:
+
+        X.Y.Z
+
+  - X is main version number
+  - Y is release number
+  - Z is patch number
+
+## Bumping numbers
+
+ One of these numbers will get bumped in each new release. The numbers to the
+ right of a bumped number will be reset to zero.
+
+ The main version number will get bumped when *really* big, world colliding
+ changes are made. The release number is bumped when changes are performed or
+ things/features are added. The patch number is bumped when the changes are
+ mere bugfixes.
+
+ It means that after release 1.2.3, we can release 2.0.0 if something really
+ big has been made, 1.3.0 if not that big changes were made or 1.2.4 if only
+ bugs were fixed.
+
+ Bumping, as in increasing the number with 1, is unconditionally only
+ affecting one of the numbers (except the ones to the right of it, that may be
+ set to zero). 1 becomes 2, 3 becomes 4, 9 becomes 10, 88 becomes 89 and 99
+ becomes 100. So, after 1.2.9 comes 1.2.10. After 3.99.3, 3.100.0 might come.
+
+ All original curl source release archives are named according to the libcurl
+ version (not according to the curl client version that, as said before, might
+ differ).
+
+ As a service to any application that might want to support new libcurl
+ features while still being able to build with older versions, all releases
+ have the libcurl version stored in the curl/curlver.h file using a static
+ numbering scheme that can be used for comparison. The version number is
+ defined as:
+
+```c
+#define LIBCURL_VERSION_NUM 0xXXYYZZ
+```
+
+ Where XX, YY and ZZ are the main version, release and patch numbers in
+ hexadecimal. All three number fields are always represented using two digits
+ (eight bits each). 1.2 would appear as "0x010200" while version 9.11.7
+ appears as "0x090b07".
+
+ This 6-digit hexadecimal number is always a greater number in a more recent
+ release. It makes comparisons with greater than and less than work.
+
+ This number is also available as three separate defines:
+ `LIBCURL_VERSION_MAJOR`, `LIBCURL_VERSION_MINOR` and `LIBCURL_VERSION_PATCH`.