support for multiple currencies

Makefile:
	addition of BTCWATCH_VERSION variable for versioning via macro at compile-time
	addition of custom CFLAGS for debug builds

btcapi.c:
	minor indentation changes
	more includes:
		stdio.h
		stdlib.h
		string.h
	exits when error detected instead of returning NULL in all functions
	code minification

cmdlineutils.c:
	help string condensed in to one multi-line printf function
	addition of -c option
	addition of -V option

main.c:
	renamed URL_API to api_url as a char[] for string manipulation
	addition of API_URL_CURRENCY_POS macro for manipulating currency in api_url
	inclusion of ctype.h, stdint.h
	indentation fixes
	implemented multiple currency support:
		"AUD"
		"CAD"
		"CHF"
		"CNY"
		"CZK"
		"DKK"
		"EUR"
		"GBP"
		"HKD"
		"JPY"
		"NOK"
		"PLN"
		"RUB"
		"SEK"
		"SGD"
		"THB"
		"USD"
	implementation of macro versioning via BTCAPI_VERSION from Makefile