Added some extension details

docs/en/manuals/extensions_details.md

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+
+# The Defold build setup
+
+Here we list some relevant build information, in order to make the integrations with your extensions as easy as possible.
+
+Here are some things to consider when you create an extension for the Defold engine.
+
+# Static linkage
+
+The custom engine is built using static linkage.
+The main reason is that on iOS, multiple executable binaries in an .ipa aren't allowed in the app store.
+
+# No Exceptions:
+
+We don't make use of any exceptions in the engine, as it decreases executable size and improves the runtime performance. This may be beneficial for you to if you wish to get a minimal extension.
+
+# C++ version
+
+In the engine itself we use no C++ version higher than C++98. While you may use a higher version to build your extension, bear in mind that a higher version might come with ABI changes. This might make it impossible to use your extension in conjunction with other extensions in the engine or on the asset store.
+
+When creating libraries (such as extensions), it's good to keep the lowest common denominator as a target.
+
+# Standard Template Libraries - STL
+
+Since the Defold engine doesn't use any STL code (except std::sort), it may work for you to use STL in your extension. Again, bear in mind that ABI incompatibilites may hinder you when using your extension in conjunction with other extensions.
+
+In the Defold engine, we use `const char*` instead of `std::string`. And writing your own dynamic array or hash table isn't very hard, but there are also good alternatives found online.
+
+# Toolchain
+
+Clang - MscOS, iOS, (Win32)
+GCC - Android, Linux (deprecated)
+CL - Windows (deprecated)
+
+_NOTE: We are aiming to compile all platforms with Clang in the near future in order to streamline our builds_
+
+## SDK Versions
+
+* Android:
+* iOS: iPhoneOS11.2.sdk
+* MacOS: MacOSX10.13.sdk
+* Windows: WindowsKits 8.1 + 10.0, Microsoft Visual Studio 14.0
+* Linux: Ubuntu 16.04, gcc 5.4.0, libssl-dev, uuid-dev, libxi-dev, libopenal-dev, libgl1-mesa-dev, libglw1-mesa-dev, freeglut3-dev
+* Html5: Emscripten 1.35.0,
+
+## C++ version + ABI compatibility
+
+We build our engine using `-std=c++98`
+
+For iOS/MacOS, we use `-miphoneos-version-min=6.0` and `-mmacosx-version-min=10.7` respectively.
+
+* Linux: `GCC 5.4.0`
+* Android:`GCC 4.8`
+* Html5: `Emscripten 1.35.0`
+* Win32: `Microsoft Visual Studio 14.0` alt `clang-6.0`
+* iOS/MacOS: `apple-clang` alt `clang-6.0`
+
+# Win32 + Clang
+
+A recent addition is to be able to build the Windows builds using clang.
+This allows for faster builds on our servers, and also it allows us to streamline our builds.
+
+_NOTE: This feature is new, so it's not enabled by default yet_
+
+You can use this feature by adding the flag `use-clang` to your app manifest:
+
+    platforms:
+        x86_64-win32:
+            use-clang: true
+
+
+## CL.exe / LINK.exe
+
+Although this feature is still supported, it will soon be deprecated.
+
+
+
+
+