Add #line directives when amalgamating sources

This is useful during development and disabled by default.
Merge pull request #169 from cesanta/amalgam

Add #line directives when amalgamating sources
Refactor and improve test Makefile

Removes duplication and cleanup output.
This greatly simplifies the reusing of this makefile from
other Cesanta C projects.

Added `compile` target which performs a blazingly fast parallel syntax only
check for multiple dialects. As the tests take longer and longer, it's becoming
frustrating to figure out that there were a syntax violation in one dialect
after 30 seconds have passed.
Merge pull request #170 from cesanta/cleanup_test_mk

Refactor and improve test Makefile
Documented ns_*_opts structures
Renamed MQTT client & broker example files
Added NS_DNS_MESSAGE ns_set_protocol_dns()
Merge pull request #171 from cesanta/mqtt_example_rename

Renamed MQTT client & broker example files
Merge pull request #172 from cesanta/dns_server_example

Added NS_DNS_MESSAGE ns_set_protocol_dns()
Readability: flags renamed
Merge pull request #173 from cesanta/flag_rename

Readability: flags renamed
Fix #174
Merge pull request #177 from cesanta/issue_174

Fix #174
Add high level DNS server helpers