Rename nvim_lsp to lspconfig

[h-michael]

resolve #97
related #334

This PR includes breaking changes as it involves changing the name of the module.
There is also a discussion in #334 about whether to remove the installer or stop using monorepo.
I think it's better to make these changes at the same time because multiple breaking changes in a short period of time can be confusing to users.

[justinmk]

LGTM

This PR includes breaking changes as it involves changing the name of the module.

Let's define a nvim_lsp module that returns an error and/or shows a :echomsg like

NOTICE: "nvim_lsp" module was renamed to "lspconfig". Update your config/plugins to require('lspconfig') instead of require('nvim_lsp').

[tjdevries]

I don't remember if we've talked about this before, but what about vim.lsp.config?

[justinmk]

I don't remember if we've talked about this before, but what about vim.lsp.config?

But it isn't part of the lsp module. It's a separate extension. So why name it like it is ? That seems actively confusing for no reason.

Lots of variants were suggested in #97

[teto]

if we target a christmas release, may be good to proceed as early as possible, even if just for the rename (nvim_lsp to lspconfig)

[h-michael]

@tjdevries @teto
Sorry for toooooo late replying. I've added a deprecated message.