Export `rl_readline_name` cell to Ruby interface

检查将应用程序名称硬编码为 (char *)"Ruby" 的 readline gem 代码以及周围的 Ruby 接口。阅读 GNU Readline 关于 rl_readline_name 的文档，并确定应如何公开它。完成的标准是 Ruby 应用程序可以设置该单元，同时当前的默认行为保持不变。

IIUIC, the rl_readline_name attribute allows per-application customisations in .inputrc. From man readline concerning the $it application/$endif construct:

application
The application construct is used to include application-specific settings.
Each program using the readline library sets the application name,
and an initialization file can test for a particular value. This could be used
to bind key sequences to functions useful for a specific program. For instance,
the following command adds a key sequence that quotes the current or
previous word in bash:

  $if Bash
  # Quote the current or previous word
  "\C-xq": "\eb\"\ef\""
  $endif

The current implementation arrogates this capability to itself, preventing its use by Ruby application developers. Currently the readline gem hard-codes this to (char *)"Ruby". However, a compiler (interpreter) isn't really an application, particularly since it itself is not using the readline library. That seems to be more appropriately the province of things written in Ruby. And then only if they choose to change it from the "Ruby" default. Note that the documentation explicitly says: "Each program using the readline library sets the application name." I offer that the Ruby interpreter binary is not "the application" by this documentation.

Therefore, this is a FREQ that this cell be exposed to the Ruby level in the gem code, allowing Ruby code developers to set this according to their own application needs.

Thanks!