user visible:
* Add VSM / VCL_error loging for parser warnings
* differenciate between real errors and warnings
* change return values of to_http0_e
* add warnings() function to query about warnings from VCL

internal:
* rename VMOD_HTTP0* to VESICO* and http0_* to vesico_*
* include a txt'ified version of phk's http_split
* rewrite vesico_analyze_cookie_header to use http_split