Add compile option overrides

[sebastiw]

CLOSES: #8

Option to override configuration per file or match pattern.

One can now specify a list of tuples with some file-pattern and the overrides it should do for that file-pattern.
Use {file, Filename} for overriding specific files, and {re, Regex} to override for all files with full path matching the regex.

Example for including another directory when compiling asn1s with similar names but different content.

{asn1_args, [
   ....
  {overrides, [
    {{file, "CAP_PHASE1.set.asn1"}, [{compile_opts, [{i, "cap_v1/"}]}]},
    {{file, "CAP_PHASE2.set.asn1"}, [{compile_opts, [{i, "cap_v2/"}]}]}
]}.

Example if the user has a directory structure containing files with different encoding.

{asn1_args, [
   ....
  {overrides, [
    {{re, "/per-files/"}, [{encoding, per}]},
    {{re, "/uper-files/"}, [{encoding, uper}]}                     
]}.

e.g. for directory structure:

• project/asn1/per-files
• project/asn1/ber-files
• project/asn1/uper-files