initial naive stencil implementation

The current stencils are limited: only up to 2 dimensions are
supported, all dimensions must be of the same size.
implement symbols
implement the symbol table
initial lex/yacc implementation
ignore lex and yacc generated *.[ch] files
Merge branch 'llama' into dev

The current syntax seems to cover all basic cases.
Merge branch 'internals' into dev

The symbol table should be ready for use.