Version 0.1.2

• Marked EcoVec::{new, is_empty, len} as const fn (thanks to @Kmeakin)
• Improved performance of EcoVec::from_elem and eco_vec! macro (thanks to @Kmeakin)
• Switched to smarter internal representation of an empty EcoVec which simplifies the code and removes a potential branch in EcoVec::as_slice for types with huge alignment (thanks to @Kmeakin)
• Added std feature (enabled by default) and impl std::io::Write for EcoVec<u8> guarded by it (thanks to @imbrem)