Add detail to the snippet completion items

[urandom]

Use the menu to add further details for any snippet completions, to help the user pick the right one without guessing.

[haorenW1025]

I personally thinks putting this information in completion menu makes the menu a little bit too long to see, especially with Neosnippets the description is often very long. That's why the information is shown in the hover windows for now.

[urandom]

On one hand, those entries could be large, which would be a problem for a small window. On the other however, relying on the hover for information is not very user friendly. One would have to go over the entries one by one in order to find the one that fits. Perhaps the "menu" text could be truncated to at most N characters, where N could either be configurable, or somehow derived from the available size, if the later is possible to be queried.

[haorenW1025]

Actually the hover window idea comes from coc.nvim, and I personally don't think that it's not user-friendly because you still need to go over the completion menu to complete anyway. Maybe I'll leave it as it is right now and if there are more people agree with your opinion then I'll try to find a good way of implement this. Sorry for any possible offend.