Replace try! macros with ? operators

…fetime

Remove unnecessary lifetime

Move travis notifications to gitter

Add Clippy to Travis

Remove unused lzw dependency

Provide bits_per_pixel and num_components as ColorType methods

png: Fix decoder off-by-1 error

Format code by rustfmt

Co-authored-by: martinlindhe

A somewhat long outstanding feature. The previous pub attribute on the
function may have made it confusing and wrongly suggested that this was
already the case.

Closes: image-rs#978

Dynimage from decoder

Fix tiff magic bytes

Fix few clippy warnings

Update crate metadata for release 0.22.2

Fix the WebP spelling in README

Does not touch the public interface, only internal `_impl` variants
which are simply referenced from their new location.

Firstly, simply renames load to decode.

Also splits open into to operations:
- open, which will inspect the file contents to guess the correct format
  *before* falling back to a path.
- from_path, which imitates the old behaviour.

Don't deprecate them just yet, for now they are even the underlying
primitives instead of being wrappers around the reader.

Fixes guess_format to only change the format on successful guesses.

Minimize the commitment of public interface for now. The builder style
methods are likely the most immediately useful.

Image reader

Failure that occurs only on nightly seems to be more often due to Rust
breakage than a bug. Take deprecation warnings more serious by actively
denying them which warns us of incompatible future versions as nightly
would.
  Note: May remove this again in the future if it doesn't help. We've
  already had the case where the rustc version commitment left us
  without a proper replacement for a while since that had only been
  introduce shortly before deprecation.

Also ensures that tests are ran on all relevant builds instead of only
on nightly.

For osx and windows targets build with the first env combination since
they are matrix includes. This ensures that this selects the build
script with default features instead of no features.

Checks if a variable was declared, not if it has a non-empty content.
The core operation `${VARNAME+word}` will equal `word` if `VARNAME` is
set and non-null and be empty otherwise.

```
 DEFAULT_FEATURES=''
 [ -z "$DEFAULT_FEATURES" ] # true
```

```
 DEFAULT_FEATURES=''
 [ -n "${DEFAULT_FEATURES+exists}" ] # false
```

Align travis build to actions

gitignore: ignore target as a symlink

An array is indexed with constants that exceed its size. This is
inopportune even in a branch that never gets executed. This changes it
so that the indexing happens on a slice.

Also removes a bunch of annotations by avoiding primitive casts with
explicit type annotations in constants.

Fix strict const_err

Use `match` instead of `if-else` chain

Lints do affects downstream libraries if they use `image` as a path
dependency. Due to the spread of the library it seems somewhat likely to
be the case somewhere.

Bump version and changelog for v0.22.3