use Vital.Bitwise.xor instead of built-in xor() function

Because built-in bitwise operation functions are introduced at 7.3.377
and they are not available before 7.3.377. So I use Vital.Bitwise.xor
instead of built-in one, which switches built-in function and an
original implementation.
Merge pull request #110 from rhysd/improve/xor128_compatibility

use Vital.Bitwise.xor instead of built-in xor() function
add Message module (ref #103)
rename Message module to Vim.Message (ref #103)
Vim.Message: add 'abort' (thanks @mattn)
Text.LTSV: fix spec: exception string is wrong
add Text.CSV module

Text.CSV(code, doc, spec) is based on Text.LTSV.
If only they can use a module which has common processes of two modules.
Process: s:spawn(): add {special} argument
add Web.URI module (import from urilib.vim)

NOTE:
* urilib.vim will be obsolete.

TODO:
* doc
Web.URI: change 'urilib' to 'Web.URI', and so on