doc: convert the documentation to the block format

The syntax overview no longer describes a line-based format, since that
is not what the rest of the documentation shows.  It now covers the
grammar, the two naming conventions, the nine aliases, and the leading
'-' on a path, and it says plainly that both formats are still read and
told apart per file by content.  Without that, a reader with an
existing configuration is left wondering what happened to it.

service-opts.md was a list of modifiers to place between a directive
and its command, so it needed rewriting rather than translating: there
are no positions left to describe.  It is now grouped by what the
settings do.

conditions.md needed correcting.  It presented '!' as a condition
prefix alongside '~'.  It is neither a condition nor a negation, it is
a flag on the block that means one thing on a service and another on a
run or task, so it is spelled reload-signal and required here, and the
page maps the old form to both.

Two things the pages claimed are not true.  The kill delay range is
1-300, not 1-60, and stop and reload scripts are no longer run without
a timeout.

ChangeLog.md keeps its line-based examples.  Those sit in historical
release entries, and rewriting them in a syntax that did not exist at
the time would misdate the format.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

doc/config/env.md

@@ -6,15 +6,16 @@ and any `*.conf`, was added.  It is worth noting that these are global
 and *shared with all* services -- the only way to have a service-local
 environment is detailed in [Services Environment](service-env.md).
 
-The syntax for global environment variables is straight forward.  In
-Finit v4.4 the `set` keyword was added for completeness, but the old
-syntax (without the `set ` prefix) is still honored:
+Global environment variables go in an `environment` block, `env` for
+short:
 
-    set foo=bar
-    set baz="qux"
+    environment {
+        foo = "bar"
+        baz = "qux"
+    }
 
 On reload of .conf files, all tracked environment variables are cleared
-so if `foo=bar` is removed from `finit.conf`, or any `finit.d/*.conf`
+so if `foo` is removed from `finit.conf`, or any `finit.d/*.conf`
 file, it will no longer be used by Finit or any new (!) started
 run/tasks or services.  The environment of already started processes can
 not be changed.