Implement a new `tool_function_bash` that executes shell commands via `popen` and captures their output into a dynamically allocated buffer. Register the corresponding `tool_description_bash` JSON schema and include it in the `tools_descriptions` array alongside the existing HTTP GET tool. Also change the history file path from `~/.calpaca_history` to `.r_history` and remove the redundant `read_history` call before adding new history entries.
Implement tool calling infrastructure including tools.h with http_fetch function description and execution, message_add_tool_call and message_add_tool_result helpers in messages.h, tool descriptions injection into user messages and chat_json, http header parsing utilities in http.h, curl_get function in http_curl.h, and tool call execution loop in openai_chat that recursively processes tool results.
