added opman, deleted extra #includes from val and man header
moved header files to seperate folder, added apt-get glib to travis.yml

header files are now in src/header, travis.yml also installs libglib2.0-dev
before running the script (will hopefully fix errors).
basic manager/opman functionality, add op, stack funcs

created add operation and have a basic addition example working (100+101)
added functions to treat GSList num_list and expr_list like stacks
added umbrella header file operators.h for including ops in manager/opman
added new files to makefile
added expr_join for concatenating two exprs (GStrings) in ops