Add vcpkg installation instructions

The second call to newlocale() with LC_TIME accidentally made things
 work because LC_TIME == LC_NUMERIC_MASK on some platforms.

Though we will no longer be comparing exactly against INT64_MAX, this is ok
because any value of that magnitude stored in a double will *also* have been
rounded up, so the comparison will work appropriately.

.travis.yml:test on more recent clang and gcc versions

Maybe something weird about how gcc is configured with the test
toolchain?

(#498)

README.md:fix 2 typos

test/Makefile.am:add missing deps for test1 and test2

json_pointer.h:suggest minor grammar improvement for pointer doc

Allows the tests to pass when running `make distcheck`

This fixes the 2 broken tests I mentioned at
https://github.com/json-c/json-c/pull/499#discussion_r306998261

build: add option --disable-werror to configure

was typod as -Wwrite-string

to omit -Werror compiler option

Install CMake module files

Installation directories empty with CMake in pkg-config.

CMake was not properly substituting the installation dir variables (they
ended up all empty), so the pkg-config results were also wrongs. For
instance cflags was: -I -I/json-c
Even though json-c was found at configure time, this obviously broke the
build of any application using it.

Convert ChangeLog to valid UTF-8 encoding.

Fix compiler warnings

Fixed misalignment in JSON string due to space after \n being printed...

json_object_private: save 8 bytes in struct json_object in 64-bit arc…