add custom texts to userOptions

[Tijawk]

Adding options to customize texts

export interface Options {
    [...],

    /**
     * Search text on navbar.
     * 
     * @default 'Search...'
     * @type string
     * @memberof Options
     */
    searchText?: string;

    /**
     * Placeholder text on search input.
     * 
     * @default 'Search. Use double quotes for stricter results.'
     * @type string
     * @memberof Options
     */
    placeholderText?: string;

    /**
     * Text to display when no results are found.
     * 
     * @default 'No results found.'
     * @type string
     * @memberof Options
     */
    noResultsText?: string;

    /**
     * Text to display when search is complete.
     * 
     * @default '{time}ms for {count} results'
     * @type string
     * @memberof Options
     */     
    searchTimeText?: string;
}

close #17

[Tijawk]

README.md needs to be updated with new options

[Tijawk]

Close this PR.

Replaced by #21 with more improvements