upgrade relx to 3.21.0

Fix Edoc cross-links in umbrella projects

Given the topological sort applied to top-level apps, we should be able
to carry the edoc values for paths configured when more than one app
exists.

This allows multiple disjoint app to have defined cross-linking in the
documentation.

Tests pending.

Print error on too many help arguments

Previously the help task would crash when given more than two
arguments. After this change it instead print a message:

    Too many arguments given. Usage: rebar3 help [<namespace>] <task>

Hookable escript

Repeats some of the steps used in the bootstrap script for non-windows
systems so that 'rebar3 escriptize' can be used in development for
faster results:

- ./bootstrap  9.95s user 1.55s system 102% cpu 11.234 total
- rebar3 escriptize  0.49s user 0.14s system 101% cpu 0.623 total

This will allow to move and modify the generated files

Fix filtering of system libraries in escriptize

Typo fix.

https://github.com/erlang/rebar3/pull/1249 introduced a mechanism by
which escript dependencies of applications only would be included; this
required adding a filter to skip system libraries in the OTP root
because that tends to break escripts in very nasty ways.

However, the problem came that some libraries are just not in the
escript path but may still be included; for these libraries the path
prefix check failed as they return `{error, bad_name}` from
`code:lib_dir(Dep)` rather than just the path they're in --
specifically, this happens with top level apps.

The issue was reported in https://github.com/erlang/rebar3/issues/1294
and the current patch fixes it by accepting a `bad_name` dep as valid,
since it is obviously not in the root path.

template_dir option was forgotten in documentation plus recurse in di…

Handle `escriptize` when the specified app is missing

Ignore IntelliJ IDEA files

This family of IDE with Erlang plugin is already quite popular.

When rebar.config contains a `escript_main_app` option, but the
specified app doesn't exist in the build directory, print an error.

ssl_verify_hostname was renamed to ssl_verify_fun

Add issue template to help people fill tickets

fix catching  `not_valid` error on dialyzer

Fix opts check when compiler called with dict opts

rebar_base_compiler allows to be called with two types of options: a
dictionary, or a rebar_state record. In the later case, the options are
taken out with a call from rebar_opts, which fetches options that have
been inserted in the application via rebar_app_info as part of the
app_discovery phase, and are a list.

This yields a possibility that options used when formatting warnings can
either be a list of a dict, and we only used lists when making checks.
This ended up breaking 3rd party compiler users (i.e. LFE compile
plugin) since they were calling us with a dict rather than our own
internal records.

This patch supports both types of lookups to avoid issues.

Relx upgrade to version 3.20.0

Add OTP 19.0 to travis

Avoid PLT rebuild when files deleted on new dialyzer

Handle empty PLT or app when using dialyzer

Escriptize based on configured apps only

Fixes for windows environment: 1) copy empty directories when cloning…

Used a nonexisting option instead of a correct one

Prior to this patch, the escriptize command flat out selected all
declared dependencies.

This patch instead looks at the app files and only includes the
dependencies of the top level app and the extra ones, avoiding to
package more apps than required.

This required a version bump on cth_readable as it mistakenly included
'syntax_lib' instead of 'syntax_tools' as a dependency.

lock file contains expected hash for pkg dependencies

Let DEBUG="" and QUIET="" mean disable the option

use logs rather than skimming github pages