Trivial: Rework some control flow for readability

Dub.fetch: Deprecate Dependency overload, only accept Version[range] ...

Because fetching a path-based or repository dependency doesn't
make much sense.

improve some output coloring ...

See #2347

change TAG_WIDTH const to a variable value ...

use it for making error-only output be more readable

Deprecate Dependency.versionSpec ...

All places which assumed that Dependency contained a VersionRange have been culled,
so we can now start removing those properties.

Overrides: Make it clear that only VersionRange can be overriden ...

The code was always assuming overrides were VersionRange,
as trying to do 'dub add-override' would call 'Dependency'
constructor with a string, which forwards to VersionRange.fromString.
However, when using dub as a library, this assumption was much less obvious,
notably because the fields are public.
With this change, we make sure library users do not misuse overrides.

Use std.sumtype for PackageOverride too ...

Like Dependency, we only were using one of those two fields,
but it was not readily obvious before, and we relied on one
of them being empty to read the other one.

make command exit codes more consistent

dub search: Improve text, rename parameter ...

The 'query' name is inaccurate, as we only ever expect a package name.

Revert "Default `dub init` to SDL" ...

This reverts commit 3d0d867.

Default `dub init` to SDL ...

Átila wants to throw out dub.json, so this is the first step to discouraging dub.json

Deprecate duplicated enum LocalPackageType -> PlacementLocation ...

Two enums, both have the same values, in the same order.

Incorporate review by Jan Jurzitza <gh@webfreak.org>.

Address review by WebFreak001.

Keep logging functionality out of the public API as requested in https://github.com/dlang/dub/pull/2124#issuecomment-813016939.

Fix/Update some tests and make some info messages more similar to original version of Dub

Fix rebase errors

Fix really stupid error in previous commit

Replace --no-colors & --force-colors with --colors={auto|on|off}

Add --force-colors option to force colors enabled

Add --no-colors option to disable colors in terminal ...

Minor: changed function name in logging module

Revert logInfo to print a single line after a fetch

Fixed project upgrade message

Output improvements in package management ...

(dub fetch and dub remove)

Now checks if the output is a console or not ...

This allows to disable colors accordingly, to avoid ASCII escape
sequences in piped output.

!!! tested only on Linux.

Also: minor documentation improvements

Fixed output of some commands ...

Some commands look ugly with the tag-based logging, now using
logInfoNoTag to print "normally" like before.

New logging module - initial functionality ...

The new module replaces dub.internal.vibecompat.core.log by using the
same function names, but implementing colored output and the left
fixed-width tag. Overloaded functions are provided to output colored
text.

Still missing initLogging() and non-TTY stdout/stderr detection

Commandline: Do not duplicate GeneratorSettings fields ...

Instead of adding fields individually to the Command, just store a GeneratorSettings,
and getopt it as needed.

Remove message about system installation of packages ...

This is no longer true, we have /var/lib/dub
Moreover, users should be familiar with this, as it's how most package managers work.

Remove long-deprecated 'install' and 'uninstall' command ...

There were deprecated before dub v1.
I stopped going up the history after 4d8f81b,
on 2013-11-13, where they were already deprecated.