more autoconf tweaks

addition of [1msrc/main.o[0m
  gcc -osrc/main.o src/main.c -c -Wall -Wextra -Wpedantic -std=gnu99 -march=native -O3

[1msrc/lib/btcapi.o[0m
  gcc -osrc/lib/btcapi.o src/lib/btcapi.c -c -Wall -Wextra -Wpedantic -std=gnu99 -march=native -O3

[1msrc/lib/libbtcapi.a[0m
  ar rc src/lib/libbtcapi.a src/lib/btcapi.o
  ranlib src/lib/libbtcapi.a

[1msrc/lib/cmdlineutils.o[0m
  gcc -osrc/lib/cmdlineutils.o src/lib/cmdlineutils.c -c -Wall -Wextra -Wpedantic -std=gnu99 -march=native -O3

[1msrc/lib/libcmdlineutils.a[0m
  ar rc src/lib/libcmdlineutils.a src/lib/cmdlineutils.o
  ranlib src/lib/libcmdlineutils.a

[1mall[0m
  gcc -obtcwatch src/main.o -Lsrc/lib/ -lbtcapi -lcmdlineutils -lcurl  -ljansson

[1minstall[0m
  install -s -m777 btcwatch /usr/bin/ target
small changes to configure.ac
makefile modularisation of targets
makefile indentation when building targets
addition of [1muninstall[0m
  rm /usr/bin/btcwatch target
allow use of environment variables in Makefile (CC, CFLAGS)