Implement job control

- Add a job control module for spawning and controlling co-processes
- Add three vimscript functions for interfacing with the module
- Use dedicated header files for typedefs/structs in event/job modules
Add BACKERS.md

List of Neovim backers provided by Bountysource
Format backers list
vim-patch:7.4.181

Problem:    When using 'pastetoggle' the status lines are not updated. (Samuel
            Ferencik, Jan Christoph Ebersbach)
Solution:   Update the status lines. (Nobuhiro Takasaki)

https://code.google.com/p/vim/source/detail?r=cb5683bcde03796baa7e845fd9a2fcaec3383538
Remove more OOM error handling code

From the functions:

 - ExpandBufnames
 - buf_modname()
 - do_autocmd_event()
 - ff_create_stack_element()
 - ff_get_visited_list()
 - ins_complete()
 - msg_show_console_dialog()
 - prt_find_resource()
 - vim_findfile_init()

TODO: refactor msg_show_console_dialog() to make sure it doesn't ever return
NULL.
Remove OOM error handling code after calls to diff_alloc_new()
Remove OOM error handling code after calls to transstr()

transstr() doesn't return NULL anymore.
Remove OOM error handling code after calls to mf_hash_grow()
Remove OOM error handling code after ga_grow() calls
No error condition in foldInsert()
alist_add_list() doesn't return -1 anymore
No error condition in get_arg_list()
No error condition in store_loop_line()
No error condition in push_current_state()