The regular font weight had a gigantic difference between normal and fat
text. Whereas for the book font weight there was barely any difference
at all.

Currently replaces frametitle icon, if both icon and subtitle are set.

Fixes font styles 'light' and 'regular', as the required font styles
were renamed upstream.

See the following upstream commits:
https://github.com/mozilla/Fira/commit/317e6c0d9a06c9b9db2a7b1281ccb7e8f983cd98
https://github.com/mozilla/Fira/commit/d6d05bf47955a36aab5d66319882b17b95944d92

This avoids looking for an internal command that will be removed
in a future update.

The fixes in
https://github.com/josephwright/beamer/commit/ef419391cbe5245cabf3b77c89b58023fb253c95
and
https://github.com/josephwright/beamer/commit/ce790e640c0b41ab3adf764a79a9ef9475e37532
mean that a new patch route is needed. Patches cannot be nested
(easily) so use two and a switch to track if an error is needed.

The command needs three arguments: \@ehc is the 'Press Enter to
continue" generic advice.

fixes #239 in some cases

Fix #212

As the theme's documentation is generated from `doc/metropolistheme.dtx` and not by running latex on the component sub-packages, this code is never actually executed. (Good thing, too, since it wouldn't compile; it is not possible to call `beamerthememetropolis` in a document with the `ltxdoc` class)

Fix #11

Fix #187

Prevents me from thinking it tests "if font sexist" instead of "if fonts exist"

Use \themename in documentation instead.

The default fontspec font features are

```
\defaultfontfeatures
 [\rmfamily,\sffamily]
 {Ligatures=TeX}

\defaultfontfeatures
 [\ttfamily]
 {WordSpace={1,0,0},
  PunctuationSpace=WordSpace}
```

There isn't a reason to override this (see PR #154).

Attention: this breaks the theme loading that is described all over the internet
by now.

beamer font definitions are now standard latex based

implemented conditional font loading scheme

added demo frame to test font features

better implementation of monospaced numbers in tables

As also suggested on
[stackexchange](http://tex.stackexchange.com/questions/112526/errors-wit
h-makeuppercase-and-beamers-insertsectionhead) the new implementation
patches `\sectionentry`, `\beamer@section` and `\beamer@@frametitle`
instead of expanding them.

In the process I also added three more hooks:

- `mthemesectiontitleformat`
- `mthemeframetitleformat`
- `mthemeplaintitleformat`

So the user can change the behavior of each element independently. As
default the new formats are dependent on `mthemetitleformat`.

For testing purposes I integrated @elliottd s frames from this PR #94

This should fix the `allowframebreaks` issue for real now.