Downloads Trend Rework

• Added linear trend line to downloads trend graph.
• Added icons marking crate features that directly include dependencies in Features Section.
• Changed the logo from PNG to SVG image.
• Changed downloads trend graph colors from D3.js' origin scheme to crates.io color scheme.
• Fixed downloads trend from normal linear graph to stack graph.
• Fixed faulty (negative) downloads trend interpolation.

Initial Pre-Release

This version is the first pre-release version, marked as alpha due to lack of thoroughly tested by the developer. The base features are well performed but still need a lot of testing results.