Compile as library and move all json rpc methods to a Connection class

[bdhobare]

Attempt 2:

Changes:

• Build the library separately as a static library (libsol). Split top-level CMakeLists into different CMakeLists for the examples, the tests and the library itself for easier management.
• Moved all json rpc calls to a Connection class that is used as entrypoint to the library and extracted the rpc implementations to solana.cpp.
• Moved all WebSocket subscription methods to the namespace solana::rpc::subscription
• Refactored the examples to use the Connection class.
• Moved all headers to the include directory and reorganized methods in the global namespace to the solana namespace

  auto connection = solana::rpc::Connection(config.endpoint);
  const auto group = connection.getAccountInfo<mango_v3::MangoGroup>(config.group);
  ...
  const auto market = connection.getAccountInfo<mango_v3::PerpMarket>(perpMarketPk.toBase58());
  ...
  const auto recentBlockhash = connection.getRecentBlockhash();

  Tests done:

• Transaction
• PlaceOrder
• SendTransaction
• ./bin/tests
• Examples

[mschneider]

the rest of the codebase is using clang-format with "Visual Studio" style, would be good to keep it in one style or change all files.