build, refactor: Use conventional version notation for boost package

Dot is used as a separator in versions of other depends packages.

depends/packages/boost.mk

@@ -1,7 +1,7 @@
 package=boost
-$(package)_version=1_71_0
-$(package)_download_path=https://boostorg.jfrog.io/artifactory/main/release/$(subst _,.,$($(package)_version))/source/
-$(package)_file_name=boost_$($(package)_version).tar.bz2
+$(package)_version=1.71.0
+$(package)_download_path=https://boostorg.jfrog.io/artifactory/main/release/$($(package)_version)/source/
+$(package)_file_name=boost_$(subst .,_,$($(package)_version)).tar.bz2
 $(package)_sha256_hash=d73a8da01e8bf8c7eda40b4c84915071a8c8a0df4a6734537ddde4a8580524ee
 $(package)_dependencies=native_b2