feat(gotests): generate tests only for exported func

docs(gotests): generate test for exported funcs

README.md

···
 :GoTestsAll
 ```
 
+Generate tests only for exported functions/methods in current file
+
+```vim
+:GoTestsExp
+```
+
 7. Run `go generate` command
 
 ```vim

lua/gopher/gotests.lua

···
   add_test(cmd_args)
 end
 
+---generate unit tests for all exported functions
+---@param parallel boolean
+function M.all_exported_tests(parallel)
+  local cmd_args = {}
+  if parallel then
+    table.insert(cmd_args, "-parallel")
+  end
+
+  table.insert(cmd_args, "-exported")
+  add_test(cmd_args)
+end
+
 return M

lua/gopher/init.lua

···
 gopher.impl = require "gopher.impl"
 gopher.generate = require "gopher.gogenerate"
 gopher.test_add = gotests.one_test
+gopher.test_exported = gotests.all_exported_tests
 gopher.tests_all = gotests.all_tests
 
 return gopher

plugin/gopher.vim

···
 command! -nargs=* GoTagRm :lua require"gopher".tags_rm(<f-args>)
 command! -nargs=* GoTestAdd :lua require"gopher".test_add(<f-args>)
 command! -nargs=* GoTestsAll :lua require"gopher".tests_all(<f-args>)
+command! -nargs=* GoTestsExp :lua require"gopher".test_exported(<f-args>)
 command! -nargs=* GoMod :lua require"gopher".mod(<f-args>)
 command! -nargs=* GoGet :lua require"gopher".get(<f-args>)
 command! -nargs=* GoImpl :lua require"gopher".impl(<f-args>)