fix and update ruby bindings

[thedavemarshall]

This introduces a few changes/fixes for the ruby bindings. While the process for building and installing the gem locally was working, I ran into some issues in another project when trying to use bundler to build the gem from the remote git source for me. I've verified these changes address those issues.

• since building the gem appears to copy the Cargo.toml and Cargo.lock files before attempting to build native extensions on the host, this fails with relative paths to regorus from regorusrb. I think this might eventually be solvable with more advanced build scripts for the ruby gem, or would eventually be solved if the gem ends up built/published as part of regorus CI and includes pre-compiled binaries for distribution. In the meantime, I'm addressing this by pointing regorusrb to depend on regorus = { git = "https://github.com/microsoft/regorus" }
• related to above, change bindings/ruby/LICENSE.txt from a symlink to a copy of LICENSE
• Update bindings/ruby/README.md to indicate the ruby gem name is regorusrb, remove bundle add command until glob option is supported, add instructions for building and installing the rubygem from source
• require 'rb-sys' in gemspec for building the gem, specify extension through extconf.rb, which will auto-install the rust toolchain if not present. Also include rake-compiler-rust gem when building and developing locally, which allows cross-compiling for different architectures, i.e. rake 'native[x86_64-linux]'
• change the output location for dynamic libraries from bindings/ruby/regorusrb/regorusb.so (or appropriate file extension) to bindings/ruby/regorus/regorusrb.so. This is more in keeping with the ruby module/namespace Regorus, while allowing referencing the dynamice library regorusrb distinctly from the regorus ruby code, which is uesful to avoid ambiguous require and require_relative statements in ruby
• add Regorus::Engine#eval_bool_query(), #eval_allow_query, and #eval_deny_query methods

[anakrish]

Thanks for the contribution!

[anakrish]

Does Ruby have a non mingw Windows target that we could use?

[anakrish]

LGTM