Enhanced installation instructions to README.rst

This commit mainly contains better installation instructions (#255).
Additionally 'Robot Framework' was made a link and trailing whitespace
removed from few places.

After writing the new instructions, I noticed that there already were
better instructions in INSTALL.rst. I decided to commit my changes anyway
because they contain better pip examples and explain proxy configuration.
Instructions in INSTALL.rst were also partly outdated.

Having these new instructions and old instructions in INSTALL.rst obviously
doesn't make any sense. We need discuss do we want to keep more detailed
instructions in README or have separate INSTALL. Let's continue that
discussion in issue #255.
Register browser even if get url fails.

An issue was reported with SeleniumLibrary [1] where if "Open Browser"
succeeds in starting the browser but the get url call fails the opened
browser doesn't get registered with the Library's internal browser registery.
Thus when 'Close All Browsers' is called it fails to close the opened browser.
This patch fixes that problem.

[1] http://code.google.com/p/robotframework-seleniumlibrary/issues/detail?id=220
Added debug log message indicating failed to open url.
Added test verifying browser closes if 'Open Browser' is incomplete.

This patch verifies the fix for #70.
Merge branch 'close-browser-on-failed-open'
Merge pull request #261 from pekkaklarck/installation-instructions

Enhanced installation instructions to README.rst
Merge pull request #263 from emanlove/master

Register browser even if get url fails.
Updated CHANGES.rst with recent commits.
Merge pull request #2 from rtomac/master

V1.5.0