Refactors CMakeLists.txt and makes it more robust

[imlk0]

The current CMakeLists.txt is problematic in that:

1. external dependencies (openssl, curl) are not checked with find_package().
2. no support for cmake's CMAKE_INSTALL_PREFIX, which may make it difficult to be integrated
3. some typos incorrectly write librats as rats-tls.

So, this commit refactors CMakeLists.txt and makes it more robust.

Details:

• LibCBOR.cmake: fix build
• CMakeLists.txt: add find openssl
• check openssl include
• check CURL_INCLUDE_DIRS
• CMakeLists.txt: add missing find_package curl
• CMakeLists.txt: using CURL::libcurl instead of CURL_*
• CMakeLists.txt: move find_package openssl to subdirectory
• CMakeLists.txt: using CMAKE_INSTALL_PREFIX instead of RATS_INSTALL_PATH
• remove find_package(OpenSSL) for wasm mode