Fix: broken tests.
Ref: remove browser related code.
Ref: no need to run `call()` on callback functions. No need to verify the callback function inside async flow.
Ref: no need to verify the SQL string. It is the job of a user.
Ref: minor tweaks to tests.
Ref: minor tweaks to tests.
Enh: no need to quote a number.
Ref: major refactoring of buffer parsers to handle server responses.
Ref: major refactoring of protocol packets to optimize the work with `Buffer`. Updated tests.
Ref: refactored the `rollback` and `commit` functions.
Enh: APIS-529, Queries queuing needs improvement. Or it is 4 times slower.

Major refactoring of queries queueing mechanism for improved
performance. Added params option to `query()` function.
Doc: updated README documentation.
New: added CUBRID 8.4.4 version to Travis.
Enh: if delimiter is not specified when formatting SQL, default to single quotes.
v2.1.0: Major refactoring of query queueing mechanism, protocol packets, buffer parsers. Added new minor features.
Merge pull request #8 from CUBRID/new_features

Major refactoring of query queueing mechanism, protocol packets, buffer parsers. Added new minor features.