Specify multiple locations of DTL template files

Added a backward compartible feature to specify `erlydtl_opts' options
for the DTL template compiler to allow inclusion of templates in different
directories with different compilation settings for each. E.g.:

    {erlydtl_opts, [
          [{doc_root, "src/view"}, {module_ext, "_dtl_vw"}]
        , [{doc_root, "src"},      {module_ext, ""}, {recursive, false}]

        , {out_dir,   "ebin"}
        , {compiler_options, [verbose, debug_info]}
    ]}.

The definition above is identical to this (the last two options
are duplicated in each list):

    {erlydtl_opts, [
          [{doc_root,   "src/view"}
          ,{module_ext, "_dtl_vw"}
          ,{out_dir,    "ebin"}
          ,{compiler_options, [verbose, debug_info]}]

        , [{doc_root,   "src"}
          ,{module_ext, ""}
          ,{out_dir,    "ebin"}
          ,{compiler_options, [verbose, debug_info]}
          ,{recursive, false}]
    ]}.

In this case "src/view" and "src" directories containing template files
will be compiled.  A new `recursive' option tells rebar_erlydtl_compiler
to search files recursively from a given doc_root.  In the example above
the "src" directory won't be scanned recursively, and the target template
name for target beam modules won't have "_dtl_vw" suffix.
Made more readable printout of the erlydtl compiler message

The printed message is made more terse.

Example before applying patch:

    ERROR: Compiling template src/view/test.dtl failed:
      {error,{"src/view/test.dtl",
              [{{4,7},
                erlydtl_parser,
                ["syntax error before: ",["\"\\\"HELLO_WORLD\\\"\""]]}]}}

Example after applying patch:

    ERROR: Compiling template "src/cmp_html_error_template.dtl" failed:
        (line:3, col:12): ["syntax error before: ",["trans"]]
Fix erlydtl dependency check

When a DTL template includes other template files, those files don't need
to be compiled separately, and therefore can be given an extension different
from `source_ext` (such as `.dtli`) to avoid being compiled.  This fix
allows rebar to find included dependencies with names `*.dtl*` rather
than `*.dtl` and properly determine if a template file needs to be recompiled.
Merge pull request #327 from saleyn/erlydtl_compiler

Erlydtl compiler
Merge pull request #328 from saleyn/depcheck

Fix erlydtl dependency check
rebar_erlydtl_compiler: fix incorrect lists:keysort/2 call
Fix Dialyzer warning in rebar:run/2
Merge pull request #14 from tuncer/fix-list-keysort-call

Fix rebar_erlydtl_compiler:erlydtl_opts/1 and rebar:run/2
Restore support for so_name, port_envs and port_sources
Add support to compile the Diameter dictionary files
Merge pull request #15 from rebar/dss-restore-ports

Restore support for so_name, port_envs and port_sources
Bumping to 2.1.0-pre
Be sure to filter empty sources (h/t to Tuncer and Joe Norton)
Add diameter exclusions to xref
Merge branch 'ates-diameter'
rebar.config.sample: fix syntax error
rebar.config.sample: fix raw dep example formatting
rebar.config.sample: fix erl_opts example
rebar_erlc_compiler: fix src_dirs comment
Merge pull request #18 from tuncer/fix-config-sample

Fix rebar.config.sample