Fix MR Selection, Go Code Refactor (#358)

refactor: Refactors the Go codebase into a more modular and idiomatic approach
fix: require selection of specific MR when there are multiple targets for a given source branch
feat: Allows for the passing of Gitlab's filter options when choosing an MR, improves MR selection
feat: API to choose an MR from a list based on the provided username's involvement as an assignee/reviewer/author

This is a #MINOR release

doc/gitlab.nvim.txt

@@ -739,22 +739,39 @@ Choose a merge request from a list of those open in your current project to
 review. This command will automatically check out the feature branch locally
 and open the reviewer pane (this can be overridden with the `open_reviewer`
 parameter.
+
 You can also filter merge requests by specifying `label` and `notlabel`
-parameters.
+parameters, or any other parameter included in list MRs API.
+
+By default, the endpoint will return all open merge requests.
 >lua
   require("gitlab").choose_merge_request()
   require("gitlab").choose_merge_request({ open_reviewer = false })
-  require("gitlab").choose_merge_request({ label = {"include_mrs_with_label"} })
-  require("gitlab").choose_merge_request({ notlabel = {"exclude_mrs_with_label"} })
+  require("gitlab").choose_merge_request({ labels = {"include_mrs_with_label"} })
+  require("gitlab").choose_merge_request({ ["[not]labels"] = {"exclude_mrs_with_label"} })
 <
     Parameters: ~
-        • {opts}: (table|nil) Keyword arguments to configure the checkout.
+        • {opts}: (table|nil)
             • {open_reviewer}: (boolean) Whether to open the reviewer after
             switching branches. True by default.
-            • {label}: (table<string>) Return merge requests with *including* matching labels
-            • {notlabel}: (table<string>) Return merge requests *excluding*
-              matching label
+            • {labels}: (table<string>) Return merge requests with *including* matching labels
+            • Etc, see: https://docs.gitlab.com/ee/api/merge_requests.html#list-merge-requests
+
+                                                                *gitlab.nvim.choose_merge_request*
+gitlab.choose_merge_request_by_username({opts}) ~
+
+Choose a merge request based on the username provided. Like the `choose_merge_request`
+action, this will automatically check out the branch locally and open the
+the reviewer pane when the MR is chosen.
+>lua
+  require("gitlab").choose_merge_request_by_username({ username = "hcramer" })
 <
+    Parameters: ~
+        • {opts}: (table|nil)
+            • {username}: (string) The username of the Gitlab user, must be a
+            member of the current project.
+            • {state} [optional]: (string) The status of the MR, e.g. "opened" or "all"
+
                                                                 *gitlab.nvim.review*
 gitlab.review() ~