chore, add travis ci config

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'next'

* next: (33 commits)
  chore, add travis ci config
  minor, allow strings in quoted lists as well
  minor, provide callbacks expected by echs-lisp.c in echse-collect.c
  minor, build collect_s objects on the way down through the lisp file, calling back things in echse-collect.c
  hygiene, use head popping when freeing colls in fini_collect()
  fix, in free_coll() actually put the coll_t object onto colls.q's free list
  minor, introduce bookkeeper list for chained gq element maps
  minor, provide gq_push_head()
  minor, adapt echse-collect to new gq pools
  minor, change gq impl again, provide single-linked-lists with push-tail and pop-head
  minor, use a simple state machine to track the grammar of a echs lisp file
  minor, import echs-lisp collection file parser (a simple lisp parser)
  fix to fix, define UNLIKELY in echs-file.c
  fix, PEBKAC, return pointer to closure in either case (in echs-file's make_echs_stream()) so free_echs_stream() can free it
  minor, massage echse-collect code to prepare collection file parsing
  minor, provide hard-coded echse-collect proof-of-concept run
  hygiene, handle NULL pointers in gq_item() and GQ_NULL_ITEMs in gq_item_ptr()
  minor, refactor popping rinsers into gq_rinse()
  minor, when popping the head of a dll, rinse the outcome
  fix, PEBKAC, use a queue's itemz slot unmodified
  ...