ini: Fix parsing of variable with spaces before the =

At least from what the source code suggests, a variable declaration in
the config file as this should be supported:
DFLAGS = -I/usr/include/d

But in reality, if you live spaces like that, the variable value will
get uppercased.

This commit fixes this problem to properly parse the extra spaces.
man: Update man to talk about dmd1.conf

Instead of talking about dmd.conf that is conflictive when you want for
both dmd1 and dmd2 to co-exist. The use of dmd.conf for dmd1 is said to
be deprecated.
man: Move dmd1.conf to docs/man/man5
man: Mention variable names are converted to uppercase
ini: Add support to define undefined variables

Similarly to Make files, the syntax `VAR ?= value` is added to define
variables only when they were previously undefined.

In this case, if the environment variable `VAR` was undefined, then it
will be defined with the value `value`, otherwise the previous content
of `VAR` will be preserved.

This is useful to define default flags in the config file that can be
easily overridden by using environment variables.
Merge pull request #3075 from leandro-lucarella-sociomantic/cond-conf-vars

ini: Add support to define undefined variables
Remove travis stuff

Both .travis.yml and the build status from the README.md are gone.
Add a brief description about what is this repo about
Add debian packaging using fpm

The Debian package is called dmd1 to make it forward-compatible with an
eventual dmd2 package. The dmd binary is still accessible through
a debian "alternative", so in the future is easy to select which
compiler to use by default.

A top-level Makefile is added to ease building, to build the Debian
package just use `make deb`.

More information about fpm:
https://github.com/jordansissel/fpm