Remove uninitialized var warnings present if -O2 is used.

Do it by initializing relevant vars to 0.

houdini_html_e.c: In function ‘houdini_escape_html0’:
houdini_html_e.c:72:11: error: ‘esc’ may be used uninitialized
                        in this function [-Werror=uninitialized]

houdini_xml_e.c: In function ‘houdini_escape_xml’:
houdini_xml_e.c:134:10: error: ‘code’ may be used uninitialized
                        in this function [-Werror=uninitialized]
Add extern "C" to header files.
Add .gitignore.
Add flexible GNU Makefile.

The default goal is creating a static library - libhoudini.a.
It makes embedding houdini in other projects even easier.

Building out of tree and using chosen directory for object files
(OBJDIR variable) is also supported.
Merge pull request #3 from przemoc/cleaning

Do some "cleaning"
Add license file
Backport into the 21st century
Unify these macros
char * all of the things
Merge pull request #5 from vmg/next

Backport into the 21st century
Revert "char * all of the things"

This reverts commit 4fda30d36eba1dc3e8d3ab7b37c7b214a6f8ab7b.
Call the cops I don't give a fuck
Small fix for URL encoding
Update API on the README