Update CONTRIBUTING.md
fix #1291
Skip test for pkg-config. test for spiroentrypoints.h and libspiro.

Some distros are not completely configured correctly for pkg-config.
There is a school of thought that argues for using PKG_CHECK_MODULES,
but that is not necessary. The standard way to check if a library
exists and to link against it is to use AC_CHECK_LIB(), and also check
for the developer header file(s) using AC_CHECK_HEADERS().

Fixed fontforge_create_pkg-config.m4 to only include libspiro as a
dependecy ONLY if it exists AND user didn't say no to include libspiro.

This comes to a hard-stop if user wants libspiro, but it's not available.
eliminate warning of implicitly defined functions
missed copy-n-paste of brackets on ${LIBSPIRO_LIBS} into git master
Skip test for pkg-config. test for uninameslist.h and libuninameslist.

Some distros are not completely configured correctly for pkg-config.
There is a school of thought that argues for using PKG_CHECK_MODULES,
but that is not necessary. The standard way to check if a library
exists and to link against it is to use AC_CHECK_LIB(), and also check
for the developer header file(s) using AC_CHECK_HEADERS().

Fixed fontforge_create_pkg-config.m4 to only include libuninameslist as
a dependecy ONLY if it exists AND user didn't say no to include it.

This comes to a hard-stop if user wants libuninameslist, but it's not
available. This also tests for version 0.3 and 0.4 of libuninameslist

Libunicodenames was placed in '#' (commented) since it was going to be a
fair bit of re-write to work-around the repeated AC_DEFINE in configure.ac
Issue #1341 recommends sticking with 1 library rather than support both,
and libunicodenames seems to be limited in function access and OS choices.
Users that want to use libunicodenames can move the comment '#' to switch
libraries for one or the other (see configure.ac) since the active code
is still in place if you want to use the other library, or if there is
another library in future, shouldn't be hard to modify for others:
FONTFORGE_ARG_WITH_LIBUNINAMESLIST
#FONTFORGE_ARG_WITH_LIBUNICODENAMES
Upgrade unicodelibinfo to work with libuninameslist-0.4.2014xxxx

Upgraded routines to take advantage of built-in 0.4 functions instead of
having to find the block count, start, end. Still remain compatible with
older versions of libuninameslist if newer version not yet available.
Added library block-count to native scripting and python scripting.
missed a copy-n-paste from working copy into git master '<='
Begin adding some more info during ./configure
Merge pull request #1400 from coolwanglu/header_fix

fix #1291
Merge pull request #1401 from JoesCat/check_headers_and_libraries

Skip test for pkg-config. test for spiroentrypoints.h and libspiro.
Fix NULL pointer crash in PSTKD_Ok().

SFDCreateUndoForLookup() returns NULL if an error occurs when
reading the file to a string.  We should not call GFileWriteAll() in
that case.
Merge pull request #1405 from blipvert/fixes/39

Fix NULL pointer crash in PSTKD_Ok().
Come to a hard-stop if user wants libreadline, but it's not available.

Default is to check and include, or not include if not available, but
if user option is "--with-libreadline" then the library and header files
must be available, otherwise ./configure comes to a hard-stop.
Merge pull request #1404 from jtanx/threading

Some code cleanup & add support for GIFLIB >= 5.1.0
Merge pull request #1406 from JoesCat/check_headers_and_libraries_readline

Come to a hard-stop if user wants libreadline, but it's not available.