Add description and homepage metadata to packages

Add a2png package

Add ascii package

Add sfk package

Add dos2unix package

Add aws package

Add valgrind package

Add descriptions and homepages to gcc related packages

Add ffmpeg package

Strip some common packages

Refactor dependency expansion

Change crew to hide `buildessential` from dependencies list since it is a fake package.
Change crew to not check :build dependencies if a target is already installed.
Chagen crew to remove unnecessary push_dependency call.
Change package.rb to update comments

Also add check method.

Adding cmatrix package

Add readline dependency to R

DEBUG_SYMBOLS modification

Update openssl to 1.0.2l and distribute with pre-built arm binaries

Update mlocate homepage url

Change openssl.rb to strip binary and libraries and prepare to install man correctly.
Also add check method to check the correctness.

  - Remove libvpx package