Build warnings on xrl and yrl files

[austin-nl]

warning: in order to compile .yrl files, you must add "compilers: [:yecc] ++ Mix.compilers()" to the "def project" section of ex_abi's mix.exs
Warning:   (mix 1.16.2) lib/mix/tasks/compile.yecc.ex:70: Mix.Tasks.Compile.Yecc.preload/1
  (mix 1.16.2) lib/mix/compilers/erlang.ex:66: Mix.Compilers.Erlang.compile/6
  (mix 1.16.2) lib/mix/task.ex:478: anonymous fn/3 in Mix.Task.run_task/5
  (mix 1.16.2) lib/mix/tasks/compile.all.ex:124: Mix.Tasks.Compile.All.run_compiler/2
  (mix 1.16.2) lib/mix/tasks/compile.all.ex:104: Mix.Tasks.Compile.All.compile/4
  (mix 1.16.2) lib/mix/tasks/compile.all.ex:93: Mix.Tasks.Compile.All.with_logger_app/2

warning: in order to compile .xrl files, you must add "compilers: [:leex] ++ Mix.compilers()" to the "def project" section of ex_abi's mix.exs
Warning:   (mix 1.16.2) lib/mix/tasks/compile.leex.ex:69: Mix.Tasks.Compile.Leex.preload/1
  (mix 1.16.2) lib/mix/compilers/erlang.ex:66: Mix.Compilers.Erlang.compile/6
  (mix 1.16.2) lib/mix/task.ex:478: anonymous fn/3 in Mix.Task.run_task/5
  (mix 1.16.2) lib/mix/tasks/compile.all.ex:124: Mix.Tasks.Compile.All.run_compiler/2
  (mix 1.16.2) lib/mix/tasks/compile.all.ex:104: Mix.Tasks.Compile.All.compile/4
  (mix 1.16.2) lib/mix/tasks/compile.all.ex:93: Mix.Tasks.Compile.All.with_logger_app/2