Share identical compilation units directly between http and stream modules

[agentzh]

Some compilations units like shdict.c, string.c, lex.c, regex.c, and etc, could share the object code directly between http and stream modules in the final nginx executable. We could simply make the http and stream lua module depend on this meta lua module not only at codegen time, but also at compile and link time :)

[agentzh]

This can make the resulting binary smaller by avoiding binary code duplication in the final executable.

[thibaultcha]

Proposal here: #76