Simplifications and cleanup to the build script

* The script now supports zsh and bash to allow building from macOS and
  Linux with builtin zsh and bash version 3 or 4.
* It now uses curl instead of wget, wget is not builtin on macOS.
* Use the default NDk path from the Android SDK.
* Allow to set custom build and output folders.
* The various build folders for each version are now kept around under
  the 'build' folder.
* At the same time add the build folder to .gitignore.
* Create relative symlinks KDAB#61.

.gitignore

@@ -0,0 +1,2 @@
+build/
+.DS_Store

README.md

@@ -4,7 +4,7 @@ OpenSSL scripts and binaries for Android (useful for Qt Android apps)
 In this repo you can find the prebuilt OpenSSL libs for Android, a QMake include project `.pri` file that can be used integrated with Qt projects, and a `.cmake` file for CMake based projects.
 
 The following directories are available
-* `ssl_3`: used for Qt 6.5.0+.
+* `ssl_3`: for Qt 6.5.0+.
 * `ssl_1_1`: for Qt Qt 5.12.5+, 5.13.1+, 5.14.0+, 5.15.0+, Qt 6.x.x up to 6.4.x
 
 ## How to use it
@@ -23,7 +23,7 @@ if (ANDROID)
     FetchContent_Declare(
       android_openssl
       DOWNLOAD_EXTRACT_TIMESTAMP true
-      URL      https://github.com/KDAB/android_openssl/archive/refs/heads/master.zip
+      URL https://github.com/KDAB/android_openssl/archive/refs/heads/master.zip
 #      URL_HASH MD5=c97d6ad774fab16be63b0ab40f78d945 #optional
     )
     FetchContent_MakeAvailable(android_openssl)
@@ -51,14 +51,11 @@ endif()
 ## Build Script
 
 The build script `build_ssl.sh` can be used to rebuild the OpenSSL libraries. Since specific
-versions might depend or work better with specific NDK versions, the OpenSSL<==>NDK version
+versions might depend or work better with specific NDK versions, the OpenSSL/NDK version
 combinations are defined in the script. Before running the script, check that the NDK paths
 are correct for your environment.
 
 ### Build Prerequisites
 
-Both Linux, macOS need `patchelf` command when building for OpenSSL 3+.
-
-Additionally, for macOS you need:
-- `bash` shell version 4+ is required
-- `wget` command
+The build script was tested against `bash` and `zsh` on Linux and macOS.
+The `patchelf` command is required when building for OpenSSL 3.