User instance methods to access username, password, and host

Helps us stay clear of typos.
Add checks for validity of credentials supplied by user
Update version to v0.2.0-beta.3
-------------------------------
Changes since v0.2.0-beta.2:
 - 834c617 Add checks for validity of credentials supplied by user
 - c9cc3c2 User instance methods to access username, password, and host
 - bb2aa17 Update version to v0.2.0-beta.2 ------------------------------- Changes since v0.2.0-beta.1:  - 0536dd5 Cleanup version display
 - 0536dd5 Cleanup version display
 - 477b6b6 Update version to v0.2.0-beta.1 ------------------------------- Changes since v0.1.8-final:  - 97d0e82 Make session[:host] a configuration setting  - ca9e66f Don't display '-final' in version  - e5f8c20 Remove script/release. It's now extracted to https://github.com/relaxdiego/tools.relaxdiego.com
 - 97d0e82 Make session[:host] a configuration setting
 - ca9e66f Don't display '-final' in version
 - e5f8c20 Remove script/release. It's now extracted to https://github.com/relaxdiego/tools.relaxdiego.com
 - dd30340 Update version to v0.1.8-final ------------------------------ Changes since v0.1.7-final:  - b3f21b4 Add checks for null data returned by the server  - 635f9fb Clarifications in README  - a8fa872 Make commit notes more readable  - 44f359b Improvements in script/release  - 93bb2ba Improvements to script/release
 - b3f21b4 Add checks for null data returned by the server
 - 635f9fb Clarifications in README
 - a8fa872 Make commit notes more readable
 - 44f359b Improvements in script/release
 - 93bb2ba Improvements to script/release
 - c83f77f Update version to v0.1.7-final -------------------------------- Changes since v0.1.6-final: 6ebd03d Improve display of pre-release version 0121532 Update script/release
 - 6ebd03d Improve display of pre-release version
 - 0121532 Update script/release
 - 600b80e Update version to v0.1.6 ------------------ Changes since v0.1.5: cde28d3 Refactor RD.displayReleases() 28427f5 Refactor RD.dataIsIncomplete() c00bd01 Move helper methods to bottom of class declaration 702eee2 Remove extraneous require in config.ru 5f99b67 Update the release script
 - cde28d3 Refactor RD.displayReleases()
 - 28427f5 Refactor RD.dataIsIncomplete()
 - c00bd01 Move helper methods to bottom of class declaration
 - 702eee2 Remove extraneous require in config.ru
 - 5f99b67 Update the release script
 - fd835ba Update version to v0.1.5
 - 9e0934a Corrections to script/release
 - 49bfd54 Update version to v0.1.4
 - 6020ab2 Update version to v0.1.3
 - c3b5c63 Fix release script
 - a4e36e7 Refactoring
 - 0677318 Version bump
 - c9f184c Display version in login form too
 - 1e7d190 Display version number
 - 918f22a Script to auto-increment version
 - 4c61b28 Corrections to README
 - 029bb60 Refactor private methods
 - 0d4762a Rename 'start' route to 'login'
 - 12e5a84 Add logout
 - 9d4064c Add progress indicator
 - d2172b3 Style modifications to dashboard
 - 12d8aa7 Rename start_form to login_form
 - c286625 Formatting fixes
 - c34d9fc Redirect to issue page in Jira
 - e2d25a3 Make release name clickable
 - 43d8b7e Get data in chunks
 - 8c7ed4d Accept start_at_index
 - 284bf5b Make ajax call reusable
 - acc49a4 UI fixes
 - 7e26e69 curl doesn't work properly if the URI is not surrounded by quotes
 - c58c39a Relax the Git version requirement
 - c65a954 Add Xcode requirements
 - 219a581 Remove irrelevant tips in README
 - dd02bf9 Add initial functionalities
 - a761f42 Add static assets
 - f4bbf1e Ignore Mac misc files
 - c538722 First iteration of the dashboard
 - 6981aba Add methods for authenticating and getting issues
 - 99a3ab6 First iteration of the app
 - 565afd6 Add instructions
 - e1a5331 Add Gemfile.lock
 - b6241eb Add .gitignore
 - 2f3b153 Add script/setup and other supporting files
 - 42a5fcc Create .rvmrc