Support encoding for cmucl's utf-16 strings

Rearrange test so that only we only conditionalize on the reasonably
smallest changes of the test.

Yason currently assumes strings can hold any possible unicode
codepoint.  But that's not true with cmucl which uses utf-16 encoding
for strings.  The following things are needed to allow yason to handle
cmucl's strings.

* encode.lisp:
  * Add cmucl-specific `escape-strint-to-stream` to handle cmucl's
    utf-16 strings; yason was assuming string can hold any codepoint.
* test.lisp:
  * Update test "stream-encode.unicode-string" for cmucl's utf-16 strings.

https://github.com/phmarek/yason/issues/74

Typo in doc.xml

Change serialze to serialize.

Fixes #53.

Restore order of alist to original JSON string

This will be used eg. for VLIME communication.

See also #36.