Use best practices for plugin loading

1. Remove strict requirement on Vim 8. Only require the necessary
   features to be present, and that Vim in running nocompatible.
2. Set cpo to Vim default to guarantee line continuation works.

README.md

@@ -16,8 +16,7 @@ commands in just over 150 lines of Vimscript.
    `QuickFixCmdPost`, and the bang operator work as expected.
 
 ## Requirements
-Vim 8 minimum compiled with `+job`, `+channel`, and of course
-`+quickfix`.
+Vim compiled with `+job`, `+channel`, and of course `+quickfix`.
 
 ## Installation
 ### Pathogen

doc/makejob.txt

@@ -10,7 +10,6 @@ great, but who don't like how calls to |:make| and |:grep| freeze the
 editor. _MakeJob_ implements asynchronous versions of the builtin
 commands in just over 150 lines of Vimscript.
 
-{only available in Vim version 8 or later}
 {only when compiled with the |channel|, |job|, and |quickfix| features}
 
 Here are your new quickfix commands.

plugin/makejob.vim

@@ -3,12 +3,12 @@
 " AUTHOR:  Daniel Moch <[email protected]>
 " VERSION: 1.1.2-dev
 "
-if exists('g:loaded_makejob') || version < 800 || !has('job') ||
-            \ !has('channel') || !has('quickfix')
+if exists('g:loaded_makejob') || !has('job') || !has('channel') || !has('quickfix') || &cp
     finish
 endif
 let g:loaded_makejob = 1
-
+let s:save_cpo = &cpo
+set cpo&vim
 let s:jobinfo = {}
 
 function! s:InitAutocmd(lmake, grep, cmd)
@@ -161,3 +161,5 @@ command! -bang -nargs=+ -complete=file GrepJob call s:MakeJob(1,0,0,<bang>0,<q-a
 command! -bang -nargs=+ -complete=file LgrepJob call s:MakeJob(1,1,0,<bang>0,<q-args>)
 command! -bang -nargs=+ -complete=file GrepaddJob call s:MakeJob(1,0,1,<bang>0,<q-args>)
 command! -bang -nargs=+ -complete=file LgrepaddJob call s:MakeJob(1,1,1,<bang>0,<q-args>)
+let &cpo = s:save_cpo
+unlet s:save_cpo