Include pencil_lib.h from pencil_compat.h

Suggested by Albert.  Having only one header file for the PENCIL
compatibility mode is better than having two files (in case a user wants
only to use PENCIL in compatibility mode, i.e. to compile his code with
a standard C compiler).  This patch includes the automatically
generated pencil_lib.h file in pencil_compat.h so that the user
does not need to think about including both.
Merge pull request #3 from rbaghdadi/fixes

Include pencil_lib.h from pencil_compat.h
Fix __pencil_maybe and __pencil_assert in compatibility mode
Merge pull request #4 from rbaghdadi/fixe_compatibility

Fix __pencil_maybe and __pencil_assert in compatibility mode
Various fixes; Converted to Autoconf+Automake+libtool project
Install PENCIL headers and runtime