added new method for percent encoding that encodes every character in string except to  "Unreserved characters". List of Unreserved characters is taken from http://en.wikipedia.org/wiki/Percent-encoding
Added tests for percent-encoded strings conversion.
Updated  include and library paths. Removed debug-specific libs and include paths.
improve calc content_length.

Signed-off-by: jack <jack.wgm@gmail.com>
improve body_size calc.

Signed-off-by: jack <jack.wgm@gmail.com>
Merge branch 'percent-encoding' of https://github.com/k-stolyarov/avhttp