Verified and updated all instructions and code examples for tarantool-c.

* Switch to YAML instead of JSON
* Add utilites for replication
* Print test-run internal errors to console

Fill IPROTO_KEY for DELETE and IPROTO_TUPLE for INSERT/REPLACE.

- Update link to configuration files
- Change number of queries and data set size
[skip ci]

Delete the previous checkpoint in sophia only if we have a new one.

Actually fix the bug and add a test case.

closes gh-1428

Fixed double call of tuple_init_field_map in update and upsert operations, fixed comments of tuple_alloc

If `default_cfg` was nil, then system will errored.

* Don't mislead users with box.cfg{} options which shouldn't be
  set under tarantoolctl.
* Mention that all data directories must have absolute paths and
  remove work_dir from example.lua (see #1406).
* Specify correct default values.

+ closes gh-1405 (right path for unix socket)
+ wrap box.cfg and loadfile with pcall
+ some variable/function scope cleanups (global -> local)
+ closes gh-1409 (check for lua syntax before running/restarting/eval server)

Ensure that every box operation can take tuple as key/tupl/operation in
both engines

 * require('console').ac(off) to disable autocompletion;
 * if completion is turned off, TAB key inserts TABs;
 * never fallback to builtin filename completion.

* Set version to {1, 6, 8} in box.space._schema
* Add 'LUA' language to built-in stored procedures

Use box.schema.upgrade() to upgrade.

./extra/schema_fill.lua and ./extra/schema_erase.lua were
moved to box.internal.bootstrap().

eio_req must be freed from req->destroy instead of req->finish.