[meta,cmake] Restructure project and introduce CMake tooling

Rearrange project to conform to current best-practices in modern C++ repo organization.

Introduce initial configuration file for the CMake meta-build system, based on the restructured organization.

cmake/Findcrypto.cmake

+# https://github.com/aws/aws-sdk-cpp/blob/main/cmake/Findcrypto.cmake
+# - Try to find LibCrypto include dirs and libraries
+#
+# Usage of this module as follows:
+#
+#     find_package(crypto)
+#
+# Variables used by this module, they can change the default behaviour and need
+# to be set before calling find_package:
+#
+# Variables defined by this module:
+#
+#  crypto_FOUND             System has libcrypto, include and library dirs found
+#  crypto_INCLUDE_DIR       The crypto include directories.
+#  crypto_LIBRARY           The crypto library, depending on the value of BUILD_SHARED_LIBS.
+#  crypto_SHARED_LIBRARY    The path to libcrypto.so
+#  crypto_STATIC_LIBRARY    The path to libcrypto.a
+
+# the next branch exists purely for cmake compatibility with versions older than 3.15. Please do not remove it before
+# we baseline on a newer version. It does not like duplicate target declarations. Work around that by checking it isn't
+# defined first.
+if (TARGET crypto OR TARGET AWS::crypto)
+    if (TARGET crypto)
+        set(TARGET_NAME "crypto")
+    else()
+        set(TARGET_NAME "AWS::crypto")
+    endif()
+
+    get_target_property(crypto_INCLUDE_DIR ${TARGET_NAME} INTERFACE_INCLUDE_DIRECTORIES)
+    message(STATUS "S2N found target: ${TARGET_NAME}")
+    message(STATUS "crypto Include Dir: ${crypto_INCLUDE_DIR}")
+    set(CRYPTO_FOUND true)
+    set(crypto_FOUND true)
+else()
+    find_path(crypto_INCLUDE_DIR
+            NAMES openssl/crypto.h
+            HINTS
+            "${CMAKE_PREFIX_PATH}"
+            "${CMAKE_INSTALL_PREFIX}"
+            PATH_SUFFIXES include
+    )
+
+    find_library(crypto_SHARED_LIBRARY
+            NAMES libcrypto.so libcrypto.dylib
+            HINTS
+            "${CMAKE_PREFIX_PATH}"
+            "${CMAKE_INSTALL_PREFIX}"
+            PATH_SUFFIXES build/crypto build lib64 lib
+    )
+
+    find_library(crypto_STATIC_LIBRARY
+            NAMES libcrypto.a
+            HINTS
+            "${CMAKE_PREFIX_PATH}"
+            "${CMAKE_INSTALL_PREFIX}"
+            PATH_SUFFIXES build/crypto build lib64 lib
+    )
+
+    if (NOT crypto_LIBRARY)
+        if (BUILD_SHARED_LIBS)
+            set(crypto_LIBRARY ${crypto_SHARED_LIBRARY})
+        else()
+            if (crypto_STATIC_LIBRARY)
+                set(crypto_LIBRARY ${crypto_STATIC_LIBRARY})
+            else()
+                set(crypto_LIBRARY ${crypto_SHARED_LIBRARY})
+            endif()
+        endif()
+    endif()
+
+    include(FindPackageHandleStandardArgs)
+    find_package_handle_standard_args(crypto DEFAULT_MSG
+            crypto_LIBRARY
+            crypto_INCLUDE_DIR
+    )
+
+    mark_as_advanced(
+            crypto_ROOT_DIR
+            crypto_INCLUDE_DIR
+            crypto_LIBRARY
+            crypto_SHARED_LIBRARY
+            crypto_STATIC_LIBRARY
+    )
+
+    # some versions of cmake have a super esoteric bug around capitalization differences between
+    # find dependency and find package, just avoid that here by checking and
+    # setting both.
+    if(CRYPTO_FOUND OR crypto_FOUND)
+        set(CRYPTO_FOUND true)
+        set(crypto_FOUND true)
+
+        message(STATUS "LibCrypto Include Dir: ${crypto_INCLUDE_DIR}")
+        message(STATUS "LibCrypto Shared Lib:  ${crypto_SHARED_LIBRARY}")
+        message(STATUS "LibCrypto Static Lib:  ${crypto_STATIC_LIBRARY}")
+        if (NOT TARGET crypto AND
+        (EXISTS "${crypto_LIBRARY}")
+        )
+            set(THREADS_PREFER_PTHREAD_FLAG ON)
+            find_package(Threads REQUIRED)
+            add_library(AWS::crypto UNKNOWN IMPORTED)
+            set_target_properties(AWS::crypto PROPERTIES
+                    INTERFACE_INCLUDE_DIRECTORIES "${crypto_INCLUDE_DIR}")
+            set_target_properties(AWS::crypto PROPERTIES
+                    IMPORTED_LINK_INTERFACE_LANGUAGES "C"
+                    IMPORTED_LOCATION "${crypto_LIBRARY}")
+            add_dependencies(AWS::crypto Threads::Threads)
+        endif()
+    endif()
+
+endif()