Fix finding the start and end of the current query. (#239)

1. start_request was searching forward from the cursor position. Adding
   'b' to the search flags fixed that.
2. Both start_request and end_request depended on the user having set
   'nowrapscan' to prevent wrapping around the end of the file. Such
   wrapping could result in finding the wrong query. Adding 'W' to the
   search flags fixed that, and removed the need for the stopline
   parameter.
3. Refactored the way last_line is used in end_request.

lua/rest-nvim/request/init.lua

@@ -193,7 +193,7 @@ local function start_request(bufnr, linenumber)
   local oldlinenumber = linenumber
   utils.move_cursor(bufnr, linenumber)
 
-  local res = vim.fn.search("^GET\\|^POST\\|^PUT\\|^PATCH\\|^DELETE", "cn")
+  local res = vim.fn.search("^GET\\|^POST\\|^PUT\\|^PATCH\\|^DELETE", "bcnW")
   -- restore cursor position
   utils.move_cursor(bufnr, oldlinenumber)
 
@@ -206,20 +206,19 @@ end
 local function end_request(bufnr, linenumber)
   -- store old cursor position
   local oldlinenumber = linenumber
+  local last_line = vim.fn.line("$")
 
   -- start searching for next request from the next line
   -- as the current line does contain the current, not the next request
-  if linenumber < vim.fn.line("$") then
+  if linenumber < last_line then
     linenumber = linenumber + 1
   end
   utils.move_cursor(bufnr, linenumber)
 
-  local next =
-    vim.fn.search("^GET\\|^POST\\|^PUT\\|^PATCH\\|^DELETE\\|^###\\", "cn", vim.fn.line("$"))
+  local next = vim.fn.search("^GET\\|^POST\\|^PUT\\|^PATCH\\|^DELETE\\|^###\\", "cnW")
 
   -- restore cursor position
   utils.move_cursor(bufnr, oldlinenumber)
-  local last_line = vim.fn.line("$")
 
   if next == 0 or (oldlinenumber == last_line) then
     return last_line