Merge pull request esl#14 from esl/fix-escaping-bug

* xml_size function was added  - calculates size of xmlel record 
* we are escaping every attribute & cdata - this allow a programmer to not think about it an possibly forget about doing this in crucial places.
* switched binary allocator: `enif_alloc_binary` -> `enif_make_new_binary`, because the first one **always** allocates refcounted binary, that leads to increased memory usage in case of small binaries. 
* after changing the allocators buffer overflow revealed. It was one byte and was able to cause seg fault of the whole VM see: df539c8
* I changed types, IMO they are more readable and consistent.
* Improved coverage

Merge pull request esl#8 from RGafiyatullin/master

exml_event.c: enif_open_resource_type for "parser_pointer" does not specify the destructor function.

Merge pull request esl#6 from esl/ietf89websockets

Infinit and auto-restarting streams. To be used with XMPP over WebSockets.

Add erts to the list of erlang.plt libraries

This solves issue of missing erlang:* functions in dialyzer output.

Translated cdata/attr escape functions to NIFs

Added attribute escape/unescape functions

Pretty printing XML elements

Merge pull request esl#1 from arcusfelis/master

Handle double inclusion of the header gracefully

Change xml element record name to xmlel

Export exml_stream:parser() type